Load measuring device for rolling bearing unit and load measuring rolling bearing unit

ABSTRACT

Revolution speeds n ca , n ib  of rolling elements  9   a   , 9   b  are sensed by a pair of revolution speed sensors  21   a   , 21   b . Also, a rotational speed n i  of a hub  2  is sensed by a rotational speed sensor  15   b . A sum “n ca +n cb ” or a difference “n ca −n i b” the revolution speeds of rolling elements  9   a   , 9   b  in double rows is calculated based on sensed signals of the revolution speed sensors  21   a   , 21   b , and then a ratio “n ca +n i b/ni” or “n ca −n cb /n i ” of this sum or difference to the rotational speed n i  is calculated. Then, the radial load or the an axial load is calculated based on the ratio “n ca +n c b/ni” or “ ca −n ib /ni”.

TECHNICAL FIELD

The present invention relates to a load measuring device for a rollingbearing unit and a load measuring rolling bearing unit, for example, arolling bearing unit used to support wheels of a mobile body such as acar, a railway vehicle, various carrier cars, and so forth. Moreparticularly, the present invention relates to a load measuring devicefor a rolling bearing unit and a load measuring rolling bearing unit,which can secure a running stability of a mobile body by measuring atleast one of a radial load and an axial load applied to the rollingbearing unit.

BACKGROUND ART

The rolling bearing unit is used to support rotatably the wheel of thevehicle with the suspension system. Also, the rotational speed of thewheel must be sensed to control various vehicle attitude stabilizingsystem such as the anti-lock brake system (ABS), the traction controlsystem (TCS), and so on. As a result, recently not only to supportrotatably the wheel with the suspension system but also to sense therotational speed of this wheel is widely carried out by the rollingbearing unit equipped with the rotational speed detection device inwhich the rotational speed detection device is incorporated into therolling bearing unit.

As the rolling bearing unit equipped with the rotational speed detectiondevice used for such purpose, a number of structures such as thestructure set forth in JP-A-2001-21577, etc. are known. The ABS or theTCS can be controlled appropriately by feeding a signal indicating therotational speed of the wheel, which is sensed by the rolling bearingunit equipped with the rotational speed detection device, to thecontroller. In this manner, the stability of the running attitude of thevehicle at the time of braking or acceleration can be assured by therolling bearing unit equipped with the rotational speed detectiondevice, nevertheless the brake and the engine must be controlled basedon full information, which have an influence on the running stability ofthe vehicle, to assure this stability under more severe conditions. Incontrast, in the case of ABS or TCS utilizing the rolling bearing unitequipped with the rotational speed detection device, the brake and theengine are controlled by sensing the slip between the tire and the roadsurface, i.e., so-called feedback control is executed. For this reason,since the control of the brake and the engine is delayed of course,though such delay is only an instant, improvement in such control isdesired from an aspect of the performance improvement under the severeconditions. Namely, in the case of the related-art structure, so-calledfeedforward control can prevent neither. generation of the slip betweenthe tire and the road surface nor so-called one-sided activation of thebrake, i.e., the event that braking powers are extremely differentbetween left and right wheels. In addition, such control cannot preventthe event that the running stability of the truck, or the like becomesworse due to its improper carrying state.

In light of such circumstances, the rolling bearing unit equipped withthe load measuring device shown in FIG. 37 is disclosed inJP-A-2001-21577. In this rolling bearing unit equipped with the loadmeasuring device in the related art, a hub 2 is fitted to the innerdiameter side of an outer ring 1. Such hub 2 couples/fixes the wheel andacts as a rotating ring and also an inner-ring equivalent member. Suchouter ring 1 is supported with the suspension system and acts as astationary ring and also an outer-ring equivalent member. This hub 2includes a hub main body 4 having a rotation side flange 3 at its outerend portion (end portion positioned on the out side in a width directionin a fitted state to the vehicle) to fix the wheel, and an inner ring 6fitted to an inner end portion (end portion positioned on the centerside in the width direction in the fitted state to the vehicle) of thehub main body 4 and fixed with a nut 5. Then, a plurality of rollingelements 9 a, 9 b are aligned respectively between double row outer ringraceways 7, 7 and double row inner ring raceways 8, 8. Such double rowouter ring raceways 7, 7 are formed on an inner peripheral surface ofthe outer ring 1 to act as a stationary side raceway respectively. Suchdouble row inner ring raceways 8, 8 are formed on an outer peripheralsurface of the hub 2 to act as a rotation side raceway respectively,such that the hub 2 can be rotated on the inner diameter side of theouter ring 1.

A fitting hole 10 for passing through the outer ring 1 in the diameterdirection is formed in a middle portion of the outer ring 1 in the axialdirection between the double row outer ring raceways 7, 7 and in anupper end portion of the outer ring 1 in the almost perpendiculardirection. Then, a round lever (rod-like) displacement sensor 11 servingas a load measuring sensor is fitted into the fitting hole 10. Thedisplacement sensor 11 is of non-contact type, and a sensing faceprovided to its top end surface (lower end surface) is opposed closelyto an outer peripheral surface of a sensor ring 12 that is fitted to themiddle portion of the hub 2 in the axial direction. When a distancebetween the sensing face and the outer peripheral surface of the sensorring 12 is changed, the displacement sensor 11 outputs a signal inresponse to an amount of change in the distance.

In the case of the rolling bearing unit equipped with the load measuringdevice constructed as above in the related art, the load applied to therolling bearing unit can be measured based on a sensed signal of thedisplacement sensor 11. In other words, the outer ring 1 supported withthe suspension system of the vehicle is pushed down by the weight of thevehicle whereas the hub 2 for supporting/fixing the wheel still acts tostay at that position as it is. Therefore, a deviation between a centerof the outer ring 1 and a center of the hub 2 is increased based onelastic deformations of the outer ring 1, the hub 2, and the rollingelements 9 a, 9 b as the weight is increased more and more. Then, adistance between a sensing face of the displacement sensor 11, which isprovided to the upper end portion of the outer ring 1, and an outerperipheral surface of the sensor ring 12 is reduced as the weight isincreased more and more. Accordingly, if the sensed signal of thedisplacement sensor 11 is fed to the controller, the load applied to therolling bearing unit which is equipped with the displacement sensor 11can be calculated based on a relational expression derived by theexperiment or the like previously, a map, or the like. Based on theloads applied to the rolling bearing units and sensed in this manner,the ABS can be controlled properly and also the driver is informed ofthe improper carrying state.

In this case, the related-art structure shown in FIG. 37 can sense arotational speed of the hub 2 in addition to the radial load applied tothe rolling bearing unit. For this purpose, a rotational speed encoder13 is fitted/fixed to the inner end portion of the inner ring 6 and alsoa rotational speed sensor 15 is secured to a cover 14 that is put on aninner end opening portion of the outer ring 1. Then, a sensing portionof the rotational speed sensor 15 is opposed to a sensed portion of therotational speed encoder 13 via a sensing clearance.

In operation of the rolling bearing unit that is equipped with the aboverotational speed detection device, an output of the rotational speedsensor 15 is changed when the rotational speed encoder 13 is revolvedtogether with the hub 2, to which the wheel is fixed, and then thesensed portion of such rotational speed encoder 13 passes through invicinity of the sensed portion of the rotational speed sensor 15. Inthis way, a frequency of an output of the rotational speed sensor 15 isin proportion to the number of revolution of the wheel. Therefore, ifthe output signal of the rotational speed sensor 15 is supplied to thecontroller (not shown) provided to the vehicle body side, the ABS or theTCS can be controlled appropriately.

The related-art structure set forth in above JP-A-2001-21577 measuresthe radial load applied to the rolling bearing unit whereas, inJP-A-3-209016, the structure for measuring a magnitude of the axial loadapplied to the rolling bearing unit via the wheel is set forth. In thecase of the related-art structure set forth in JP-A-3-209016, as shownin FIG. 38, the rotation side flange 3 used to support the wheel isfixed to an outer peripheral surface of an outer end portion of a hub 2a that acts as the rotating ring and the inner ring equivalent member.Also, double row inner ring raceways 8, 8 that correspond to a rotationside raceway respectively are formed on an outer peripheral surface ofthe middle portion or the inner end portion of the hub 2 a.

Meanwhile, a stationary side flange 17 to support/fix the outer ring 1to a knuckle 16 constituting the suspension system is fixed to an outerperipheral surface of the outer ring 1, which is arranged around the hub2 a in a concentric manner with this hub 2 a and acts as the stationaryring and the outer ring equivalent member. Also, the double row outerring raceways 7, 7 that correspond to a stationary side racewayrespectively are formed on the inner peripheral surface of the outerring 1. Then, a plurality of rolling elements (balls) 9 a, 9 b areprovided rotatably between the outer ring raceways 7, 7 and the innerring raceways 8, 8 respectively, whereby the hub 2 a is supportedrotatably on the inner diameter side of the outer ring 1.

In addition, a load sensor 20 is affixed to portions that surroundscrewed holes 19, into which a bolt 18 is screwed respectively to couplethe stationary side flange 17 with the knuckle 16, at plural locationson the inner side surface of the stationary side flange 17 respectively.In a state that the outer ring 1 is supported/fixed to the knuckle 16,these load sensors 20 are held between the outer surface of the knuckle16 and the inner surface of the stationary side flange 17.

In the case of such load measuring device for the rolling bearing unitknown in the related art, when the axial load is applied between thewheel (not shown) and the knuckle 16, the outer surface of the knuckle16 and the inner surface of the stationary side flange 17 are pressedagainst respective load sensors 20 from both surfaces in the axialdirection. Therefore, the axial load applied between the wheel and theknuckle 16 can be sensed by summing up measured values of these loadsensors 20. Also, in JP-B-62-3365 that, although not shown, the methodof calculating the revolution speed of the rolling elements based on avibration frequency of the outer ring equivalent member, a part of whichhas a low rigidity, and then measuring the axial load applied to therolling bearing unit is set forth.

Out of the structures that measure the load (the radial load or theaxial load) applied to the rolling bearing, as described above, in thecase of the first example of the related-art structure shown in aboveFIG. 37, the load applied to the rolling bearing unit is measured bymeasuring respective displacements of the outer ring 1 and the hub 2 inthe radial direction by means of the displacement sensor 11. In thiscase, because an amount of displacement in the radial direction isminute, a high-precision sensor must be used as the displacement sensor11 to measure the load with good precision. Since a high-precisionnon-contact type sensor is expensive, it is inevitable that a cost isincreased as the overall rolling bearing unit equipped with the loadmeasuring device.

Also, in the case of the structure for measuring the axial load as thesecond example of the related-art structures shown in FIG. 38, the loadsensors 20 must be provided to the knuckle 16 as many as the bolts 18used to support/fix the outer ring 1. For this reason, in addition tothe fact that the load sensor 20 itself is expensive, it is inevitablethat a cost of the overall load measuring device for the rolling bearingunit is considerably increased. Also, in the method set forth inJP-B-62-3365, the rigidity of the outer ring equivalent member must bereduced partially and thus there is such a possibility that it isdifficult to assure the endurance of the outer ring equivalent member.

DISCLOSURE OF THE INVENTION

An object of the present invention is to provide a load measuring devicefor a rolling bearing unit and a load measuring rolling bearing unit,capable of being constructed at a low cost with no trouble withendurance and also measuring one or both of the radial load and theaxial load applied to the wheel while assuring a precision required tocontrol. Also, another object of the present invention is to provide astructure that can sense precisely the axial load applied to the rollingbearing unit by using only an output signal of a sensor provided to arolling bearing unit portion.

A load measuring device for a rolling bearing unit according to a firstaspect of the present invention, comprises: a stationary ring having tworows of raceways; a rotating ring arranged concentrically with thestationary ring, the rotating ring having two rows of raceways which areformed respectively to be opposite to the raceways of the stationaryring; a plurality of rolling elements provided rotatably between theraceways of the stationary ring and the rotating ring, wherein contactangles of the rolling elements are directed mutually oppositely betweena pair of raceways formed on the stationary ring and the rotating ringwhich are opposite to each other and the other pair of raceways formedon the stationary ring and the rotating ring which are opposite to eachother; a pair of revolution speed sensors for sensing revolution speedsof the rolling elements in the two rows respectively; and a calculatorfor calculating a load applied between the stationary ring and therotating ring based on sensed signals fed the revolution speed sensors.

Also, a load measuring rolling bearing unit according to a second aspectof the present invention, comprises: a stationary ring having two rowsof raceways; a rotating ring arranged concentrically with the stationaryring, the rotating ring having two rows of raceways which are formedrespectively to be opposite to the raceways of the stationary ring; aplurality of rolling elements provided rotatably between the raceways ofthe stationary ring and the rotating ring, wherein contact angles of therolling elements are directed mutually oppositely between a pair ofraceways formed on the stationary ring and the rotating ring which areopposite to each other and the other pair of raceways formed on thestationary ring and the rotating ring which are opposite to each other;and a pair of revolution speed sensors for sensing revolution speeds ofthe rolling elements in the two rows respectively.

The load measuring device for the rolling bearing unit and the loadmeasuring rolling bearing unit of the present invention constructed asabove is capable of measuring the load (one or both of the radial loadand the axial load) loaded to the rolling bearing unit by sensing therevolution speeds of the rolling elements in a pair of rows, directionof the contact angles of which are different mutually, respectively. Inother words, when the radial load is applied to the rolling bearing unitlike the double row angular contact ball bearing, the contact angles ofthe rolling elements (balls) are changed. As well known in the technicalfield of the rolling bearing, the revolution speeds of the rollingelements are changed when the contact angles are changed.

Meanwhile, when the axial load is applied to the rolling bearing unit,the revolution speeds of the rolling elements in the row positioned onthe side that supports the axial load are decelerated while therevolution speeds of the rolling elements in the row positioned on theopposite side are accelerated in the case that the outer ring equivalentmember is the rotating ring. Conversely, the revolution speeds of therolling elements in the row positioned on the side that supports theaxial load are accelerated while the revolution speeds of the rollingelements in the row positioned on the opposite side are decelerated inthe case that the inner ring equivalent member is the rotating ring. Atthe same time, the revolution speeds of the rolling elements inrespective rows are changed in response to the radial load. Therefore,the radial load applied to the rolling bearing unit can be detected bymeasuring change in the revolution speeds of the rolling elements in towrows.

In particular, in the case of the present invention, since therevolution speeds of the rolling elements in a pair of rows, directionsof the contact angles of which are different mutually, are sensed, ameasuring precision of the radial load can be improved by eliminatingthe influence of the axial load. In other words, when the axial load isapplied, the revolution speeds of the rolling elements in one row andthe revolution speeds of the rolling elements in the other row arechanged in the opposite direction mutually (one is increased and theother is decreased). Therefore, the influence of the axial load upon ameasured value of the radial load can be suppressed small by adding ormultiplying these revolution speeds of the rolling elements in bothrows.

The above explanation is made of the case that the radial load appliedto the rolling bearing unit is detected, but the axial load is detectedbased on the revolution speeds of the rolling elements in a pair ofrows, directions of the contact angles of which are different mutually.In other words, the contact angles become large in the row on the sidethat supports the axial load when the axial load is increased, while thecontact angles become small in the row on the opposite side when theaxial load is increased. Then, in the case that the outer ringequivalent member is the rotating ring, the revolution speeds of therolling elements in the row positioned on the side that supports theaxial load are decelerated while the revolution speeds of the rollingelements in the row positioned on the opposite side are accelerated.Conversely, in the case that the inner ring equivalent member is therotating ring, the revolution speeds of the rolling elements in the rowpositioned on the side that supports the axial load are acceleratedwhile the revolution speeds of the rolling elements in the rowpositioned on the opposite side are decelerated. Therefore, the axialload applied to the rolling bearing unit can be detected by measuringchange in the revolution speeds of the rolling elements in two rows.

In particular, in the case of the present invention, since therevolution speeds of the rolling elements in a pair of rows, directionsof the contact angles of which are different mutually, are sensed, ameasuring precision of the axial load can be improved by eliminatinginfluences of the preload and the radial load. In other words, thepreload is applied uniformly to the rolling elements in each row and theradial load is also applied substantially uniformly. Therefore,influences of the preload and the radial load upon the revolution speedsof the rolling elements in respective rows become substantially equal.As a result, if the axial load is sensed based on a ratio or adifference of the revolution speeds of the rolling elements inrespective rows, influences of the preload and the radial load upon ameasured value of the axial load can be suppressed small.

In this case, if the rolling bearing unit is used in a state that therotational speed of the rotating ring is always constant, only therevolution speed sensors for sensing the revolution speeds of therolling elements in respective rows are required for the revolutionsensors used to calculate the load. In contrast to this, when therotational speed of the rotating ring is changed in operation, the axialload and the radial load can be measured based on the rotational speedof the rotating ring sensed by the rotational speed sensor and therevolution speeds. In this case, if a speed ratio as a ratio of thedifference (sum) between the revolution speeds of the rolling elementsin both rows to the rotational speed is calculated and then the axialload (radial load) is sensed based on this speed ratio, the axial load(radial load) can be measured exactly even though the rotational speedof the rotating ring is changed.

Also, even when the load to be detected is the radial load or the axialload or both of them, the inexpensive speed sensors used widely to getthe control signals of ABS or TCS in the related art can be used as therevolution speed sensors used to measure the revolution speeds. For thisreason, the overall load measuring device for the rolling bearing unitcan be constructed inexpensively.

Therefore, although the load measuring device can be constructed at arelatively low cost, such load measuring device can measure the loadsuch as the radial load, the axial load, etc. applied to the rotatingmember of the wheels, etc. while keeping a precision required for thecontrol. As a result, the load measuring device of the present inventioncan contribute to higher performance of various vehicle runningstabilizing devices or various machine equipments.

Also, in the implementation of the present invention, preferably theload measuring device of the present invention further comprises arotational speed sensor for sensing a rotational speed of the rotatingring.

According to such configuration, even when the rotational speed of therotating ring is changed in operation, one or both of the radial loadand the axial load can be measured precisely based on the rotationalspeed of the rotating ring sensed by the rotational speed sensor and therevolution speeds.

Also, in the implementation of the present invention, at least onesensor of the pair of revolution speed sensors and the rotational speedsensor may be a passive type magnetic sensor that is formed by winding acoil around a yoke made of magnetic material.

In other words, it is preferable that the magnetic sensor whose outputis changed in response to change in the magnetic characteristic of therevolution speed encoder rotated together with the revolution of therolling elements or the rotational speed encoder rotated together withthe rotating ring should be employed as the revolution speed sensors andthe rotational speed sensor used to implement the present invention. Assuch magnetic sensor, there are the active type into which the magneticsensing element such as Hall element, magneto resistive element, or thelike, whose characteristics are changed in response to change in themagnetism, is incorporated and the above passive type in the relatedart. The active type that can assure an amount of change in output fromthe low-speed rotation is preferable in an aspect to measure exactly therevolution speed or the rotational speed of the low-speed rotation, butis expensive at present rather than the passive type sensor. Therefore,if the passive type of a relatively low cost is used as a part ofsensors that are not particularly important to assure the reliability insensing the speed in the low-speed rotation (e.g., revolution speedsensor), a cost of the overall load measuring system for the rollingbearing unit can be suppressed.

In this case, when either the active type sensor is used or the passivetype sensor is used, the sensor equipped with the permanent magnet andthe no-magnetized encoder (tone wheel) can be used in combination toreduced a cost. As such encoder, the encoder which is made of magneticmaterial such as iron, or the like and on a sensed surface of whichthrough holes or unevennesses are provided alternately at an equalinterval in the circumferential direction may be employed. Also, inplace of such encoder, the encoder in which unevennesses are providedalternately at an equal interval on a sensed surface of a retainer madeof iron in the circumferential direction, or the encoder in whichunevennesses are provided similarly on a sensed surface of the retainermade of synthetic resin and then magnetic material is plated on theuneven surface may be employed.

Alternately, at least one sensor of the pair of revolution speed sensorsand the rotational speed sensor may be a resolver.

If the resolver is used as the sensor, the number of times of outputchange of the sensor (the number of pulses) per revolution can beincreased rather than the active type or passive type magnetic sensor.As a result, a responsibility to sense the revolution speed or therotational speed can be improved (a sensing timing of the revolutionspeed or the rotational speed can be set closer to a real time) and thusthe running stability of the mobile body can be assured based on themeasured load with higher precision.

Also, in the implementation of the present invention, preferably thepair of revolution speed sensors and the rotational speed sensor areprovided at an interval in an axial direction of the stationary ring soas to put the rolling elements in one row between the pair of revolutionspeed sensors and the rotational speed sensor.

According to such configuration, magnetic interference between a pair ofrevolution speed sensors and the rotational speed sensor can besuppressed small and also the reliability in sensing the revolutionspeed and the rotational speed can be improved.

In this case, for example, the pair of revolution speed sensors arefitted to center portions of the stationary ring in the axial directionbetween a pair of rows of the rolling elements, and the rotational speedsensor is fitted to an end portion of the stationary ring in the axialdirection.

According to such configuration, an inner diameter of the fitting holeformed in the stationary ring to install a pair of revolution speedsensors therein can be suppressed small and also assurance of therigidity and the strength of the stationary ring can be facilitated.

Also, in the implementation of the present invention, preferably a pairof revolution speed sensors and the rotational speed sensor are fittedto a top end portion of a single sensor unit fixed to the stationaryring between a pair of rows of the rolling elements. Then, a fittedposition of the rotational speed sensor is deviated closer to a rotatingring side than the revolution speed sensors in a diameter direction ofthe stationary ring.

According to such configuration, magnetic interference between a pair ofrevolution speed sensors and the rotational speed sensor can besuppressed small and also the reliability in sensing the revolutionspeed and the rotational speed can be improved. Also, an inner diameterof the fitting hole formed in the stationary ring to install the sensorunit therein can be suppressed small and also assurance of the rigidityand the strength of the stationary ring can be made easy.

Also, in the implementation of the present invention, preferably thestationary ring includes a connector for connecting a plug, the plugbeing provided to an end portion of a harness for taking out the sensedsignals of respective sensors.

According to such configuration, the harness is fitted to the rollingbearing unit by fitting the rolling bearing unit equipped withrespective sensors constituting the load measuring device to thesuspension system and then connecting the plug to the connector. As aresult, the harness becomes a bar to fit the rolling bearing unit to thesuspension system, and thus the fitting operation can be facilitated andin addition generation of a trouble such as breakage of the insulatinglayer, disconnection, etc. in the harness can be made hard. Also, eventhough the harness is damaged, only exchange of the harness and the plugis needed in the repairing operation and thus a cost required for therepair can be suppressed low.

In the case to employ such configuration, preferably the single sensorunit has a sensor holder for holding the respective sensors, and theconnector is provided integrally with the sensor holder.

According to such configuration, the connector can be fitted easily tothe stationary ring.

Also, in the implementation of the present invention, for example, onlya pair of revolution speed sensors are provided but the rotational speedsensor for sensing the rotational speed of the rotating ring is notprovided. In this case, control such as ABS, TCS, or the like to beexecuted based on the rotational speed of the rotating ring is executedbased on the rotational speed of the rotating ring, which is estimatedbased on a sensed signal of at least one revolution speed sensor out ofthe revolution speed sensors.

According to such configuration, a cost and an install space of thesensor itself can be achieved because of omission of the rotationalspeed sensor, and also a cost and an install space can be achievedbecause of reduction in the number of the harnesses to transmit thesignal.

In this case, for example, an average value of the revolution speeds ofthe rolling elements in two rows, which is calculated based on thesensed signals of the pair of revolution speed sensors, is used as anestimated value of the rotational speed of the rotating ring.

According to such configuration, even when the large axial load isapplied, the rotational speed of the rotating ring can be sensed whileassuring a precision necessary for the control such as ABS, TCS, or thelike.

In this case, in the case that the rotational speed sensor is omitted inthis manner, when the axial load is calculated based on a ratio of therevolution speeds in one row and the revolution speeds in the other row,for example, estimation of the rotational speed of the rotating ringbased on the sensed signals of the revolution speed sensors is notrequired since the axial load can be calculated irrespective of changein the rotational speed of the rotating ring.

In this case, in the implementation of the present invention, the loadapplied between the stationary ring and the rotating ring is a radialload, for example.

In this event, for example, the calculator calculates the radial loadapplied between the stationary ring and the rotating ring based on a sumof the revolution speed of the rolling elements in one row and therevolution speed of the rolling elements in the other row.

According to such configuration, the radial load can be calculated withsatisfactorily good precision.

Alternately, preferably the load measuring device of the presentinvention further comprises a rotational speed sensor for sensing arotational speed of the rotating ring. Then, the calculator calculatesthe radial load applied between the stationary ring and the rotatingring based on a sensed signal fed from the rotational speed sensor andsensed signals fed from the revolution speed sensors.

In this case, for example, the calculator calculates the radial loadapplied between the stationary ring and the rotating ring based on aratio of the sum of (a) the revolution speed of the rolling elements inone row and (b) the revolution speed of the rolling elements in theother row, and the rotational speed of the rotating ring.

Alternately, the calculator calculates the radial load applied betweenthe stationary ring and the rotating ring based on a ratio of a productof (a) the revolution speed of the rolling elements in one row and (b)the revolution speed of the rolling elements in the other row, and asquare of the rotational speed of the rotating ring.

According to such configuration, even when the rotational speed of therotating ring is changed, the radial load can be calculated with goodprecision.

Also, in the implementation of the present invention, the load appliedbetween the stationary ring and the rotating ring is an axial load, forexample.

In this case, for example, the calculator calculates the axial loadapplied between the stationary ring and the rotating ring based on aratio of the revolution speed of the rolling elements in one row and therevolution speed of the rolling elements in the other row.

According to such configuration, even when the rotational speed of therotating ring is changed, the axial load can be calculated withmaintaining necessary precision.

Alternately, the calculator calculates the radial load applied betweenthe stationary ring and the rotating ring based on a difference betweenthe revolution speed of the rolling elements in one row and therevolution speed of the rolling elements in the other row.

According to such configuration, the axial load can be calculated withmaintaining necessary precision so far as the rotational speed of therotating ring is constant.

Alternately, preferably the load measuring device of the presentinvention further comprises a rotational speed sensor for sensing arotational speed of the rotating ring. Then, the calculator calculatesthe axial load applied between the stationary ring and the rotating ringbased on a sensed signal fed from the rotational speed sensor and sensedsignals fed from the revolution speed sensors.

In this case, for example, the calculator calculates the axial loadapplied between the stationary ring and the rotating ring based on aratio of the difference between (a) the revolution speed of the rollingelements in one row and (b) the revolution speed of the rolling elementsin the other row, and the rotational speed of the rotating ring.

According to such configuration, even when the rotational speed of therotating ring is changed, the axial load can be calculated with keepingsufficient precision.

Alternately, the calculator calculates the axial load applied betweenthe stationary ring and the rotating ring based on a synthesized signalderived by synthesizing a signal representing the revolution speed ofthe rolling elements in one row and a signal representing the revolutionspeed of the rolling elements in the other row.

In this case, for example, the calculator calculates the axial loadbased on any one of a period and a frequency of a swell of thesynthesized signal.

According to such configuration, the number of harnesses fortransmitting signals from a plurality of sensors provided to the rollingbearing unit side to a controller provided to the vehicle body side canbe reduced, and a lower cost can be attained.

Alternately, preferably the load measuring device of the presentinvention further comprises a rotational speed sensor for sensing arotational speed of the rotating ring. Then, the calculator calculatesthe axial load based on a ratio of any one of the period and thefrequency of the swell of the synthesized signal and the rotationalspeed of the rotating ring.

According to such configuration, the number of harnesses can be reduced,and the axial load can be calculated with keeping sufficient precisioneven when the rotational speed of the rotating ring is changed.

Also, in the implementation of the present invention, preferably oneraceway ring of the stationary ring or the rotating ring is an outerring equivalent member, the other raceway ring is an inner ringequivalent member, respective rolling elements are balls. Then,back-to-back combination contact angles are affixed to plural balls thatare provided between a double row angular contact inner ring racewayformed on an outer peripheral surface of the inner ring equivalentmember and a double row angular contact outer ring raceway formed on aninner peripheral surface of the outer ring equivalent member.

Since such structure has large rigidity and large change in therevolution speeds of respective balls based on the load, the loadapplied between the outer ring equivalent member and the inner ringequivalent member can be measured with good precision while assuring afunction of supporting stably the wheel.

Also, in the implementation of the present invention, for example, therevolution speeds of the rolling elements in the two rows can bemeasured directly.

In this case, since the revolution speed encoder is omitted, reductionin weight and reduction in cost can be attained based on reduction inthe number of parts.

Otherwise, the revolution speeds of the rolling elements in the two rowsare measured as rotational speeds of retainers for holding respectiverolling elements.

In this case, the rotational speeds of the retainers are measured bycoupling and fixing the retainer and an encoder, which is formedseparately from the retainer, and concentrically mutually and opposingsensing portions of the revolution speed sensors to a sensed surface ofthe encoder

Alternately, the retainer is formed integrally with an elastic memberinto which powders made of magnetic material are mixed and is magnetizedto arrange alternately an S pole and an N pole at an equal interval on asensed surface, whose center corresponds to a rotation center of theretainer, out of any surfaces of the retainer, and sensing portions ofthe revolution speed sensors are opposed to a sensed surface to measurethe rotational speed of the retainer.

In this manner, if the structure for measuring the revolution speeds ofrespective rolling elements as the rotational speed of the retainer isemployed, a sensing precision of the revolution speed can be improved.

In this case, if the structure using the encoder is employed, preferablyan inner diameter of the encoder is larger than an inner diameter of afitting surface, to which the encoder is fitted, of the holder and anouter diameter of the encoder is smaller than an outer diameter of thefitting surface.

According to such configuration, the structure that can measure therevolution speeds the rolling elements with good precision whilepreventing the interference between the encode and the stationary ringand the rotating ring can be realized.

Also, if the structure for measuring the revolution speeds of therolling elements as the rotational speed of the retainer is employed,preferably the revolution speed sensors for the revolution speeds of therolling elements in two rows respectively are arranged in a state thatthe sensors are shifted in a revolution direction of the rollingelements by plural pieces every row.

In this case, preferably the revolution speed sensors are provided bytwo pieces every row on opposite positions by 180 degree with respect toa revolution center of the rolling elements.

According to such configuration, if a center of the retainer is deviatedfrom a center of a pitch circle diameter of the rolling elements andthus the retainer performs a whirling motions, the rotational speed ofthe retainer, i.e., the revolution speeds of the rolling elements can beexactly measured.

Also, preferably the load measuring device of the present inventionfurther comprises a comparator for comparing contact angles of therolling elements in each row, which are calculated by the calculator ina course of calculation of the revolution speeds of the rolling elementsin each row, with a normal value, and an alarm is generated when thecomparator decides that the contact angles are out of a normal range.

According to such configuration, the repair can be applied by sensingapplication of the excessive axial load, generations of preloadescapement, etc., which lead to reduction in the endurance of therolling bearing unit, before the vehicle falls into an impossible stateof running.

Also, in the implementation of the present invention, preferably therolling elements are made of ceramics.

If the rolling elements using ceramics, which is lighter in weight thanthe normal bearing steel, as material of the rolling elements are used,the follow-up characteristic of change in the rotation speed of therolling elements to the sudden variation of the revolution speeds can beimproved and also the revolution speeds can be measured precisely tosuppress generation of the revolution slip.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view showing s first embodiment of the presentinvention.

FIG. 2 is an enlarged view of an A portion in FIG. 1.

FIG. 3 is a view of a part of a retainer and a revolution speed sensoron the left side in FIG. 2 when viewed in a diameter direction.

FIG. 4 is a schematic view explaining an action of the presentinvention.

FIG. 5 is a diagram showing relationships among a radial load, a ratioof a revolution speed of a rolling element in each row to a rotationalspeed of an inner ring, and an axial load.

FIG. 6 is a diagram showing relationships among the radial load, a ratioof a sum of revolution speeds of rolling elements in each row to therotational speed of the inner ring, and an axial load.

FIG. 7 is a diagram showing relationships between the radial load and aratio of the revolution speed of the rolling element in each row to therotational speed of the inner ring.

FIGS. 8A and 8B are diagrams showing an influence of a magnitude of apreload or the radial load upon the relationship between the axial loadand the ratio of the revolution speed of the rolling element in any rowwhen no regard is paid to variation in the preload or the radial load.

FIGS. 9A and 9B are diagrams showing the influence of a magnitude of thepreload or the radial load upon the relationship between the axial loadand the ratio of the revolution speed of the rolling element in each rowin the present invention.

FIGS. 10A and 10B are diagrams showing relationships between adifference in the revolution speeds of rolling elements in a pair ofrows or a ratio of this difference to a rotational speed of a rotatingring and a magnitude of the axial load in the present invention.

FIG. 11 is a diagram showing relationships among a ratio of therevolution speeds of the rolling elements in a pair of rows to therotational speed of the rotating ring, a magnitude of the axial load,and a magnitude of the preload.

FIG. 12 is a diagram showing relationships among a ratio of a differencein the revolution speeds of the rolling elements in a pair of rows tothe rotational speed of the rotating ring, a magnitude of the axialload, and a magnitude of the preload.

FIG. 13 is a flowchart showing such a situation that the axial load iscalculated by synthesizing output signals of both revolution speedsensors when the output signals of a pair of revolution speed sensorsare changed in a sine-wave fashion.

FIG. 14 is a view showing the output signals of a pair of revolutionspeed sensors and a synthesized signal in this case.

FIG. 15 is a flowchart showing such a situation that the axial load iscalculated by synthesizing output signals of both revolution speedsensors when the output signals of a pair of revolution speed sensorsare changed in a pulse fashion.

FIG. 16 is a view showing the output signals of a pair of revolutionspeed sensors and a synthesized signal in this case.

FIG. 17 is a schematic view showing a revolution speed encoder andrevolution speed sensors in a second embodiment of the present inventionwhen viewed in an axial direction.

FIG. 18 is a diagram explaining the reason why the revolution speed canbe derived exactly in the second embodiment.

FIG. 19 is a view showing, similarly to FIG. 17, the case that only onerevolution speed sensor is provided.

FIG. 20 is a diagram explaining the reason why a difference in therevolution speeds derived in this case is caused.

FIG. 21 is a sectional view showing another example of a structure inwhich a pair of revolution speed sensors are provided.

FIG. 22 is a block diagram showing an example of a circuit formonitoring the revolution speed to generate an alarm when suchrevolution speed is wrong.

FIG. 23 is a partial sectional view showing a fifth embodiment of thepresent invention.

FIG. 24 is a partial sectional view showing a sixth embodiment of thesame.

FIG. 25 is a sectional view showing a first example of a seventhembodiment of the same.

FIG. 26 is a sectional view showing a structure different from theseventh embodiment.

FIG. 27 is a sectional view showing a second example of the seventhembodiment of the present invention.

FIG. 28 is a partial sectional view showing an eighth embodiment of thesame.

FIG. 29 is a sectional view showing a first example of a ninthembodiment of the same.

FIG. 30 is a sectional view showing a second example of the ninthembodiment of the same.

FIG. 31 is a sectional view showing a tenth embodiment of the presentinvention.

FIG. 32 is a sectional view showing a first example of an eleventhembodiment of the same.

FIG. 33 is a sectional view showing a second example of the eleventhembodiment of the same.

FIG. 34 is a sectional view showing a first example of a twelfthembodiment of the present invention.

FIG. 35 is a sectional view showing a second example of the twelfthembodiment of the same.

FIG. 36 is a sectional view showing a third example of the twelfthembodiment of the same.

FIG. 37 is a sectional view showing a first example of the structure inthe related art.

FIG. 38 is a sectional view showing a second example of the same.

In the drawings, 1 denotes an outer ring, 2, 2 a denote hub, 3 denotes arotation-side flange, 4 denotes a hub main body, 5 denotes a nut, 6denotes am inner ring, 7 denotes am outer ring raceway, 8 denotes aninner ring raceway, 9, 9 a, 9 b denote rolling element, 10, 10 a denotefitting hole, 11 denotes a displacement sensor, 12 denotes a sensorring, 13, 13 a, 13 b denote rotational speed encoder, 14 denotes acover, 15, 15 b denote rotational speed sensor, 16 denotes a knuckle, 17denotes a stationary side flange, 18 denotes a bolt, 19 denotes ascrewed hole, 20 denotes a load sensor, 21 a, 21 b denote revolutionspeed sensor, 22, 22 a, 22 b denote retainer, 23, 23′, 23 a denotesensor unit, 24 denotes a top end portion, 25 denotes a rimportion, 26,26 a, 26 b denote revolution speed encoder, 27 denotes an outer ring, 28denotes an inner ring, 29 denotes an outer ring raceway, 30 denotes aninner ring raceway, 31 denotes a cover, 32 denotes a space, 33 denotesan arithmetic circuit, 34 denotes a memory, 35 a, 35 b denotecomparator, 36 a, 36 b denote alarm, 37 denotes a connector, 38 denotesa harness, 39 denotes a plug, 40 denotes a slinger, 41 denotes amagnetic sensing element, 42 denotes a permanent magnet, 43 denotes ayoke, 44 denotes a coil, 45 denotes a rotor, and 46 denotes a stator.

BEST MODE FOR CARRYING OUT THE INVENTION First Embodiment

FIGS. 1 to 3 show s first embodiment of the present invention. Thepresent embodiment shows the case that the present invention is appliedto a rolling bearing unit to support idler wheels of the car (frontwheels of FR car, RR car, MR car, rear wheels of FF car). Since thestructure and the operation of this rolling bearing unit itself aresimilar to the related-art structure shown in above FIG. 37, theirredundant explanation will be omitted or simplified by affixing the samereference symbols to the same portions. Feature portions in the presentembodiment will be explained mainly hereinafter.

The rolling elements (balls) 9 a, 9 b are rotatably provided in doublerows (two rows) respectively between the double row angular contactinner ring raceways 8, 8 and the double row angular contact outer ringraceways 7, 7 in a state that a plurality of rolling elements are heldin each row by retainers 22 a, 22 b respectively. Such inner ringraceways 8, 8 are formed on the outer peripheral surface of the hub 2 asthe rotating ring and the inner ring equivalent member to constitute therotation side raceway respectively. Such outer ring raceways 7, 7 areformed on the inner peripheral surface of the outer ring 1 as thestationary ring and the outer ring equivalent member to constitute thestationary side raceway respectively. Thus, the hub 2 is supportedrotatably on the inner diameter side of the outer ring 1. In this state,contact angles α_(a), α_(b) (FIG. 2) that are directed mutually in theopposite direction and have the identical magnitude are applied to therolling elements 9 a, 9 b in respective rows to construct a back-to-backcombination type double row angular contact ball bearing. The sufficientpreload is applied to the rolling elements (balls) 9 a, 9 b inrespective rows to such an extent that such preload is not lost by theaxial load applied in operation. In the use of such rolling bearingunit, the stationary side flange 17 fixed to the outer ring 1 issupported/fixed to the knuckle constituting the suspension system, andalso a brake disk and a wheel are supported/fixed to the rotation-sideflange 3 of the hub 2 by plural stud bolts and plural nuts.

A fitting hole 10 a is formed in the middle portion of the outer ring 1constituting such rolling bearing unit in the axial direction betweenthe double row outer ring raceways 7, 7 to pass through this outer ring1 in the diameter direction. Then, a sensor unit 23 is inserted intothis fitting hole 10 a inwardly from the outside along the diameterdirection of the outer ring 1 to project a top end portion 24 of thesensor unit 23 from the inner peripheral surface of the outer ring 1. Apair of revolution speed sensors 21 a, 21 b and a rotational speedsensor 15 b are provided to this top end portion 24.

The revolution speed sensors 21 a, 21 b are used to measure therevolution speeds of the rolling elements 9 a, 9 b aligned in doublerows. A sensing surface of these sensors is arranged on both sidesurfaces of the top end portion 24 in the axial direction (the lateraldirection in FIGS. 1 and 2) of the hub 2 respectively. In the case ofthe present embodiment, the revolution speed sensors 21 a, 21 b sensethe revolution speeds of the rolling elements 9 a, 9 b arranged indouble rows as the revolution speeds of the retainers 22 a, 22 b. Thus,in the case of the present embodiment, rim portions 25, 25 constitutingthese retainers 22 a, 22 b are arranged on the mutual opposing side.Then, revolution speed encoders 26 a, 26 b formed like a circular ringrespectively are affixed/supported to mutual opposing surfaces of therim portions 25, 25 around their full circumference. The characteristicsof sensed surfaces of the revolution speed encoders 26 a, 26 b arechanged alternately at an equal interval in the circumferentialdirection such that the revolution speeds of the retainers 22 a, 22 bcan be sensed by the revolution speed sensors 21 a, 21 b.

Therefore, sensing surfaces of the revolution speed sensors 21 a, 21 bare opposed closely to mutual opposing surfaces serving as sensedsurfaces of the revolution speed encoders 26 a, 26 b. In this case, itis preferable that distances (sensing clearances) between the sensedsurfaces of the revolution speed encoders 26 a, 26 b and the sensingsurfaces of the revolution speed sensors 21 a, 21 b should be set largerthan pocket clearances defined as clearances between inner surfaces ofpockets in the retainers 22 a, 22 b and rolling contact surfaces of therolling elements 9 a, 9 b but 2 mm or smaller. If such sensingclearances are smaller than the pocket clearances, there is apossibility that the sensed surfaces and the sensing surfaces are rubbedmutually when the retainers 22 a, 22 b are displaced by such pocketclearances, and therefore such sensing clearances are not preferable. Onthe contrary, if such sensing clearances exceed 2 mm, it becomesdifficult to measure precisely revolutions of the revolution speedencoders 26 a, 26 b by the revolution speed sensors 21 a, 21 b.

Meanwhile, the rotational speed sensor 15 b is used to measure therotational speed of the hub 2 as the rotating ring. A sensing surface ofthis sensor is arranged on a top end surface of the top end portion 24,i.e., an inner end surface of the outer ring 1 in the diameterdirection. Also, a cylindrical rotational speed encoder 13 a isfitted/fixed in the middle portion of the hub 2 between the double rowangular contact inner ring raceways 8, 8. A sensing surface of therotational speed sensor 15 b is opposed to the outer peripheral surfaceof the rotational speed encoder 13 a as the sensed surface. Thecharacteristic of the sensed surface of the rotational speed encoder 13a is changed alternately at an equal interval in the circumferentialdirection such that the rotational speed of the hub 2 can be sensed bythe rotational speed sensor 15 b. The sensing clearance between theouter peripheral surface of the rotational speed encoder 13 a and thesensing surface of the rotational speed sensor 15 b is suppressed 2 mmor smaller.

In this case, as the above encoders 26 a, 26 b, 13 a, the encoder havingvarious structures used in the related art to sense the rotational speedof the wheel in order to get the control signal for the ABS or the TCSmay be employed. For example, the encoder made of a mutipolar magnet, inwhich an N pole and an S pole are arranged alternately on the sensedsurface (the side surface or the outer peripheral surface), may bepreferably employed as the above encoders 26 a, 26 b, 13 a. In thiscase, the encoder made of simple magnetic material, the encoder whoseoptical characteristic is changed alternately at an equal interval overthe circumferential direction (if such encoder is combined with themagnetic rotational speed sensor having the permanent magnet or theoptical rotational speed sensor) may also be employed.

In the case of the present embodiment, a circular-ring permanent magnetin which the N pole and the S pole are aligned alternately at an equalinterval on the axial-direction surface as the sensed surface isemployed as the above revolution speed encoders 26 a, 26 b.

Such revolution speed encoders 26 a, 26 b are formed by the insertmolding or the two color molding (two type materials are moldedsimultaneously) after they are coupled/fixed to side surfaces of the rimportions 25, 25 of the retainers 22 a, 22 b by the bonding or they areset in the cavity when these retainers 22 a, 22 b are to beinjection-molded. Any method may be employed in response to a cost,bonding strength required, etc.

If the fixing method by using the adhesive is employed, a new mold isnot needed to mold the retainers 22 a, 22 b because the ordinaryretainer in the related-art is used as the retainers 22 a, 22 b, andthus a cost can be suppressed from this aspect. Therefore, the fixingmethod by using the adhesive is effective in the case that the number ofproductions is relatively small and a cost must be suppressed as awhole. As the adhesive in this case, the epoxy adhesive or the siliconeresin adhesive can be used preferably.

In contrast, if the method of coupling/fixing the retainers 22 a, 22 band the revolution speed encoders 26 a, 26 b by the insert molding isemployed, the step of adhering the retainers 22 a, 22 b and therevolution speed encoders 26 a, 26 b is omitted, and thus a cost can besuppressed from an aspect of reduction in the assembling man-hour.

Also, separation of the retainers 22 a, 22 b and the revolution speedencoders 26 a, 26 b due to deterioration of the adhesive, etc. can beprevented without fail, and thus improvement in the reliability can beachieved. As a result, the coupling/fixing method by using the insertmolding is effective in the case that the number of productions isrelatively large and a cost must be suppressed as a whole.

Even if the retainers 22 a, 22 b and the revolution speed encoders 26 a,26 b are coupled/fixed by any method out of the adhesive and the insertmolding, the retainer formed of a synthetic resin by the injectionmolding is used as the retainers 22 a, 22 b. As the synthetic resin usedin this case, any synthetic resin may be used if such resin may bemolded by the injection molding. But polyamide 46 (PA46), polyamide 66(PA66), polyphenylene sulfide (PPS), and so on, which can secure easilythe reliability because of its excellent heat resistance and has a lowfriction coefficient, are preferable. Also, it is preferable from anaspect of improvement in the strength of the retainers 22 a, 22 b that areinforcing agent such as glass fiber, carbon fiber, or the like shouldbe mixed appropriately in the synthetic resin. As an amount of mixtureof the reinforcing agent in this case, about 5 to 40 wt % isappropriate. An effect of increasing the strength by the mixture isseldom expected if an amount of mixture is below 5 wt %, while toughnessof resultant retainers 22 a, 22 b is lowered to generate readily thedamage such as fragment, crack, or the like if the reinforcing agent ismixed in excess of 40 wt %. In order to assure the strength and thetoughness of the cases 22 a, 22 b, an amount of mixture of thereinforcing agent is restricted in a range of about 10 to 30 wt %.

Also, as the circular-ring permanent magnet used as the revolution speedencoders 26 a, 26 b, following magnets may be used. That is, thesintered magnet such as ferrite magnet, iron-neodymium magnet,samarium-cobalt magnet, or the like, the metallic magnet such asaluminum-manganese magnet, Alnico magnet, or the like, and the plasticmagnet or the rubber magnet in which magnetic powders are mixed into thesynthetic resin or the rubber can be employed. Because the sinteredmagnet and the metallic magnet give a strong magnetic force but causethe damage such as fragment, crack, or the like, the plastic magnet orthe rubber magnet should be employed preferably.

A mixing rate of the magnetic powders into the plastic magnet or therubber magnet is set to 20 to 95 wt %. Because the magnetic force of themagnet becomes strong as an amount of mixture is increased, an amount ofmixture is adjusted in response to the magnetic force required for therevolution speed encoders 26 a, 26 b , while taking account of therelationship with the performance of the revolution speed sensors 21 a,21 b. In this case, if an amount of mixture is set below 20 wt %, it isdifficult to get the magnetic force required for the revolution speedencoders 26 a, 26 b irrespective of the performance of the usedrevolution speed encoders 26 a, 26 b. In contrast, if the magneticpowders are mixed in excess of 95 wt %, it is difficult to secure thestrength of the resultant revolution speed encoders 26 a, 26 b becausean amount of the synthetic resin or the rubber as the binder is reducedexcessively. Thus, with regard to these situations, an amount of mixtureof the magnetic powders should be set to 20 to 95 wt %, preferably 70 to90 wt %. In case the plastic magnet is coupled/fixed to the retainer bythe insert molding, the coupling strength between the plastic magnet andthe retainer can be enhanced by forming the plastic magnet and theretainer with the same type synthetic resin.

Although not shown, in case the number of products is increased furthermore, it is effective from aspects of cost reduction and reliabilityimprovement to provide a function of the encoder to the retainer itself.In this case, as the synthetic resin constituting the retainer, anyresin may be employed if such resin may be molded by the injectionmolding. Like the above case that the retainer is formed as a separatebody from the encoder, assurance of the reliability can be facilitatedby using the synthetic resin such as PA46, PA66, PPS, or the like havingthe excellent heat resistance. Also, like the case that the retainer isformed separately from the encoder, it is preferable from an aspect ofstrength improvement in the retainer to mix the reinforcing agent suchas glass fiber, carbon fiber, or the like appropriately. If an amount ofthe reinforcing agent mixed into the synthetic resin constituting theretainer is too large, toughness of the resultant retainer is loweredand the damage such as fragment, crack, or the like is easily caused. Asa result, even when the reinforcing agent is mixed, an amount of mixtureis restricted in a range of 5 to 40 wt %, preferably 10 to 30 wt %.

In case a function of the encoder is provided to the retainer itself,the magnetic powders are mixed in the above synthetic resin by about 20to 95 wt %. As the magnetic powders, powders of ferrite, iron-neodymium,samarium-cobalt, aluminum-manganese, Alnico, iron, or the like may beemployed. If the retainer is formed while mixing such magnetic powers,the magnetic force of the magnet becomes stronger as an amount ofmixture is increased. Therefore, an amount of mixture is adjusted inanswer to the magnetic force required for the retainer with regard tothe performance of the revolution speed sensors 21 a, 21 b. In thiscase, an amount of the synthetic resin is reduced excessively if anamount of mixture is increased too much, and thus it becomes difficultto assure the strength of the resultant retainer (the toughness islowered). With regard to these situations, it is preferable that a totalamount of mixture of the magnetic powers and the reinforcing agentshould be suppressed smaller than 98 wt %. If the magnetic powers andthe reinforcing agent are mixed in total in excess of 98 wt %, thestrength of the retainer is lowered and also flowability of thesynthetic resin during the injection molding becomes worse, so that itis hard to get the case with good quality.

In this case, the retainer can be formed by molding the thermosettingresin such as the epoxy resin, or the like by means of the compressionmolding, independent of the event that either the retainers and therevolution speed encoders formed separately are coupled with each otheror a function of the encoder is provided to the retainer itself. In thiscase, the retainer having the excellent strength can be obtained, but acost is increased. Therefore, it is preferable that, if reduction in amass-production cost is taken into consideration, the retainer should beformed of the thermosetting resin by using the injection molding in anycase. In addition, unevenness may be formed on a part of the retainermade of the magnetic material and then such portions may be used as therevolution speed encoder. In this case, the sensor into which thepermanent magnet is incorporated to generate the magnetic flux is usedas the revolution speed sensors 21 a, 21 b. Further, unevenness can beformed on a part of the retainer made of the permanent magnetic and alsothe uneven portions can be magnetized to have the S pole and the N pole.In this case, the concave portions may be magnetized to have the S poleor the N pole and the convex portions may be magnetized to have the Npole or the S pole, otherwise only the convex portions may be magnetizedto have the S pole and the N pole alternately.

Also, as the revolution speed sensors 21 a, 21 b and the rotationalspeed sensor 15 b all being a sensor of sensing the revolution speed,the magnetic revolution sensor is used preferably. Also, as thismagnetic revolution sensor, the active type revolution sensor into whichthe magnetic sensing element such as Hall element, Hall IC, magnetoresistive element (MR element, GMR element), MI element, or the like isincorporated is used preferably. In order to construct the active typerevolution sensor into which the magnetic sensing element isincorporated, for example, one side surface of the magnetic sensingelement comes into contact with one end surface of the permanent magnetin the magnetization direction directly or via a stator made of magneticmaterial (when an encoder made of magnetic material is used), while theother side surface of the magnetic sensing element is opposed closely tothe sensed surfaces of the encoders 26 a, 26 b, 13 a directly or via thestator made of magnetic material. In the case of the present embodiment,the permanent magnetic on the sensor side is not needed since theencoder made of the permanent magnetic is used.

In the case of the load measuring device for the rolling bearing unit inthe present embodiment, sensed signals of the above sensors 21 a, 21 b,15 b are input into a calculator (not shown). This calculator may beinstalled integrally with the rolling bearing unit by providing to thesensor unit 23 in which these sensors 21 a, 21 b, 15 b areembedded/supported, or the like, or may be installed separately from therolling bearing unit on the vehicle body side. Then, this calculatorcalculates one or both of the radial load and the axial load appliedbetween the outer ring 1 and the hub 2, based on the sensed signal fedfrom these sensors 21 a, 21 b, 15 b. First the sensing of the radialload will be explained hereunder, and then the sensing of the axial loadwill be explained hereunder

In the case of the present embodiment, in order to sense the radialload, the calculator calculates a sum of the revolution speeds of therolling elements 9 a, 9 b in respective rows, which are sensed by therevolution speed sensors 21 a, 21 b, and then calculates the radial loadbased on a ratio of this sum to the rotational speed of the hub 2, whichis sensed by the rotational speed sensor 15 b. When constructed likethis, the radial load can be sensed with good precision whilesuppressing small the influence of the axial load applied to the rollingbearing unit. This respect wili be explained with reference to FIGS. 4to 6 hereunder. In this case, following explanation will be made underthe assumption that the contact angles α_(a), α_(b) of the rollingelements 9 a, 9 b in respective rows are set equal mutually in a statethat no axial load F_(a) is applied.

FIG. 4 shows the applying state of the loads to the schematic rollingbearing unit for supporting the wheel shown in above FIG. 1. Thepreloads F_(o), F_(o) are applied to the rolling elements 9 a, 9 barranged in double rows between the double row inner ring raceways 8, 8and the double row outer ring raceways 7, 7. Also, the radial load F_(r)is applied to the rolling bearing unit by the weight of the vehiclebody, etc. during operation. In addition, the axial load F_(a) isapplied by the centrifugal force applied during the turning operation,etc. All the preloads F_(o), F_(o), the radial load F_(r), and the axialload F_(a) have the influence on the contact angles α(α_(a),α_(b)) ofthe rolling elements 9 a, 9 b. Then, when the contact angles α_(a),α_(b) are changed, the revolution speed n_(c) of the rolling elements 9a, 9 b is changed. This revolution speed n_(c) is given byn _(c)={1−(d·cosα/D)·(n _(i)/2)}+{1+(d·cos α/D)(n _(o)/2)}   (1)where

-   -   D: diameter of a pitch circle of the rolling elements 9 a, 9 b ,    -   d: diameter of the rolling elements 9 a, 9 b ,    -   n_(i): rotational speed of the hub 2 to which the inner ring        raceways 8, 8 are provided, and    -   n_(o) : rotational speed of the outer ring 1 to which the outer        ring raceways 7, 7 are provided.

As apparent from this Eq. (1), the revolution speed n_(c) of the rollingelements 9 a, 9 b is changed in response to the change of the contactangles α(α_(a), α_(b)) of the rolling elements 9 a, 9 b, but the contactangles α_(a), α_(b) are changed in response to the radial load F_(r) andthe axial load F_(a), as described above. Therefore, the revolutionspeed n_(c), is changed in response to the radial load F_(r) and theaxial load F_(a). In the case of the present embodiment, since the hub 2is rotated but the outer ring 1 is not rotated, particularly therevolution speed n_(c) becomes slow with an increase of the radial loadF_(r). As a result, the radial load F_(r) can be sensed based on therevolution speed n_(c).

Here, the contact angles a followed by the change in the revolutionspeed n_(c) are changed by not only the radial load F_(r) but also thepreloads F_(o), F_(o) and the axial load F_(a). Also, the revolutionspeed n_(i) is changed in proportion to the rotational speed ni of thehub 2. For this reason, if no regard is paid to the preloads F_(o),F_(o), the axial load F_(a), and the rotational speed n_(i), it isimpossible to sense precisely the revolution speed n_(c). Since thepreloads F_(o), F_(o), are not changed in response to the driving state,it is easy to eliminate the influence by the initialization, or thelike. In contrast, since the axial load F_(a) and the rotational speedn_(i) of the hub 2 are changed constantly in response to the drivingstate, it is impossible to eliminate the influence by theinitialization.

In light of such circumstances, in the case of the present embodiment,the influence of the axial load F_(a) is reduced by calculating a sum ofthe revolution speeds of the rolling elements 9 a, 9 b in respectiverows sensed by the revolution speed sensors 21 a, 21 b. In addition, theinfluence of the rotational speed n_(i) of the hub 2 is eliminated bycalculating the radial load F_(r) based on a ratio of this sum and therotational speed n_(i) of the hub 2 sensed by the rotational speedsensor 15 b.

For example, as shown in FIG. 4, in the case that the axial load F_(a)is applied leftward in FIG. 4, relationships between revolution speedsn_(ca), n_(cb) of the rolling elements 9 a, 9 b constituting respectiverows and the rotational speed n_(i) of the hub 2 are given in FIG. 5.First, if the axial load F_(a) is 0 (the axial load F_(a) is notapplied), the revolution speeds n_(ca), n_(cb) of the rolling elements 9a, 9 b constituting respective rows are set equal mutually(n_(ca)=n_(cb)), as indicated by a solid line a in FIG. 5. In contrast,if the axial load F_(a) is applied slightly (middle level), therevolution speed n_(cb) of the rolling elements 9 b, 9 b constitutingthe right side row in FIG. 4, which support the axial load F_(a), isincreased slightly rather than the case the axial load F_(a) is 0, asindicated by a broken line b in FIG. 5. On the contrary, the revolutionspeed nca of the rolling elements 9 a, 9 a constituting the left siderow in FIG. 4, which do not support the axial load F_(a), is decreasedslightly rather than the case the axial load F_(a) is 0, as indicated bya broken line c in FIG. 5. Then, if the axial load F_(a) is increasedfurther (large level) , an amount of change of the revolution speedsn_(ca), n_(cb) is increased rather than the case the axial load F_(a) is0, as indicated by chain lines b, c in FIG. 5. In this case, the eventthat the preload is still applied to the rolling elements 9 a, 9 b thatdo not support the axial load F_(a) is assumed as the condition.

An extent Δn_(cb) to which the revolution speed n_(cb) of the rollingelements 9 b, 9 b constituting the row that support the axial load F_(a)is accelerated and an extent Δn_(ca) to which the revolution speedn_(ca) of the rolling elements 9 b, 9 b constituting the row that do notsupport the axial load F_(a) is decelerated are almost equal and theirpolarities are opposite (|Δn_(cb)|≈|Δn_(ca)|, Δn_(cb)+Δn_(ca) ≈0).Therefore, the influence of the axial load F_(a) can be substantiallyeliminated by adding the revolution speeds n_(ca), n_(cb) in both rows.FIG. 6 shows relationships among a ratio {(n_(ca)+n_(cb))/n_(i)} of asum of the revolution speeds n_(ca), n_(cb) of the rolling elements 9 a,9 b in both rows to the rotational speed n_(i) of the hub 2, a magnitudeof the radial load F_(r), and a magnitude of the axial load Fa. Asapparent from FIG. 6, if the radial load F_(r) is sensed based on a sumof the revolution speeds n_(ca), n_(cb) in both rows, the influence ofthe axial load F_(a) can be suppressed minutely and also the radial loadF_(r) can sensed exactly.

The above explanation is made to suppress the influence of the axialload F_(a) by adding the revolution speeds n_(ca), n_(cb) in both rows.In this case, the influence of the axial load F_(a) can also besuppressed by multiplying the revolution speeds n_(ca), n_(cb) in bothrows (calculating a product). In other words, since the revolutionspeeds n_(ca), n_(cb) in both rows are increased or decreased to thealmost same extent by the change in the axial load F_(a), the influencecaused by the change in the axial load F_(a) can be reduced bymultiplying the revolution speeds n_(ca), n_(cb) in both rows. Moreparticularly, the radial load F_(r) is calculated based on a ratio{(n_(ca)×n_(cb)) /n_(i) ²} of a product (n_(ca)×n_(cb)) of therevolution speeds n_(ca), n_(cb) in both rows to a square of therotational speed n_(i) of the hub.

Next, the sensing of the axial load will be explained with reference toFIGS. 7 to 16 in addition to above FIGS. 1 to 4 hereunder. In the caseof the present embodiment, in order to sense the axial load, thecalculator calculates a difference between the revolution speeds of therolling elements 9 a, 9 b in both rows sensed by the revolution speedsensors 21 a, 21 b and then calculates the axial load based on a rationof this difference to the rotational speed of the hub 2 sensed by therotational speed sensor 15 b. When constructed in this manner, theinfluences of the preload applied to the rolling elements 9 a, 9 b inboth rows and the radial load applied to the rolling bearing unit can besuppressed small, and thus the axial load can be sensed with goodprecision.

As explained with reference to above FIG. 4 and Eq.(1), the revolutionspeed n_(c) of the rolling elements 9 a, 9 b is changed in response tothe change in the contact angles α(α_(a), α_(b)) of the rolling elements9 a, 9 b. In this case, as described above, the contact angles α arechanged in response to the axial load F_(a). Therefore, the revolutionspeed n_(c) is changed in response to the axial load F_(a). In the caseof the present embodiment, since the hub 2 rotates but the outer ring 1does not rotate, the revolution speed n_(cb) of the rolling elements 9b, 9 _(b) constituting the right side row in FIG. 4 that support theaxial load F_(a) is accelerated where as the revolution speed n_(ca) ofthe rolling elements 9 a, 9 a constituting the left side row in FIG. 4that do not support the axial load F_(a) is decelerated when the axialload F_(a) is increased larger. FIG. 7 shows the changing state of therevolution speed of the rolling elements 9 a, 9 b in both rows with thechange in the axial load F_(a). Also, an axis of abscissa in FIG. 7denotes a magnitude of the axial load F_(a) and an axis of ordinatedenotes a ratio “n_(c)/n_(i)” of the revolution speed n_(c) to therotational speed n_(i) of the hub 2. In this case, a value representingthe ratio “n_(c)/n_(i)” on the axis of ordinate in FIG. 7 is increaseddownwardly in FIG. 7 and decreased upwardly.

Out of two lines a, b depicted in FIG. 7, a solid line a indicates aratio “n_(ca)/n_(i)” of the revolution speed n_(ca) of the rollingelements 9 a, 9 a constituting the left side row in FIG. 4 that do notsupport the axial load F_(a), while a broken line b indicates a ratio“n_(cb)/n_(i)” of the revolution speed n_(cb) of the rolling elements 9b, 9 b constituting the right side row in FIG. 4 that supports the axialload F_(a). In this case, the solid line a and the broken line b in FIG.7 indicate relationships between a magnitude of the axial load F_(a) anda ratio “n_(c)/n_(i)” of the revolution speed n_(c) (n_(ca), n_(cb)) tothe rotational speed n_(i) of the hub 2 in the state that the properpreload F₀ (middle level) is applied to the rolling elements 9 a, 9 b inboth rows and the radial load F_(r) is not applied (F_(r)=0).

As appreciated from the solid line a and the broken line b depicted inFIG. 7, when the axial load is applied to the double row angular contactball bearing in which the preload F₀ is applied to the rolling elements9 a, 9 b, the revolution speeds of the rolling elements 9 a, 9 b in bothrows are changed in accordance with (in almost proportion to)amagnitudeof the axial load. Accordingly, if other matters, i.e., thepreload F₀ and the radial load F_(r) acting as a crosstalk component ofthe axial load, are not considered (otherwise the preload F₀ and theradial load F_(r) are assumed constant), the axial load can be detectedby measuring the revolution speed n_(ca) (n_(cb)) of the rollingelements 9 a, 9 a (or 9 b, 9 b) in any one row.

In this event, actually the preload F₀ applied to the double row angularcontact ball bearing is varied due to manufacturing errors, and also theradial load F_(r) becomes different due to difference in the number ofpassengers and a carrying capacity.

FIG. 8 shows influences of variation of the preload F₀ and a magnitudeof the radial load F_(r) upon the relationship between a magnitude ofthe axial load F_(a) and a ratio “n_(ca)/n_(i)” of the revolution speedn_(ca) of the rolling elements 9 a, 9 a constituting the left side rowin FIG. 4 that do not support this axial load F_(a). A solid line a abroken line b, and a chain line c depicted in FIG. 8A, 8B respectivelycorrespond to the solid line a in FIG. 5 respectively. Also, FIG. 8Ashows the influence of the value of the preload F₀ upon the relationshipbetween a magnitude of the axial load F_(a) and the ratio“n_(ca)/n_(i)”. In this case, a value on an axis of ordinate in FIG. 8Arepresenting the magnitude of the ratio “n_(ca)/n_(i)” is increaseddownwardly in FIG. 8A and is decreased upwardly. Also, the radial loadF_(r) is not applied (F_(r)=0). In FIG. 8A, the solid line a indicatesthe case the preload F₀ is small, the broken line b indicates the casethe preload F₀ is at a middle level, and the chain line c indicates thecase the preload F₀ is at a large level. In contrast, FIG. 8B shows theinfluence of the value of the radial load F_(r) upon the relationshipbetween a magnitude of the axial load F_(a) and the ratio“n_(ca)/n_(i)”. In this case, a value on an axis of ordinate in FIG. 8Brepresenting the magnitude of the ratio “n_(ca)/n_(i)” is increaseddownwardly in FIG. 8B and is decreased upwardly. Also, the value of thepreload F₀ is set at a middle level. In FIG. 8B, the solid line aindicates the case the radial load F_(r) is large {F_(r)=4900 N (500kgf)}, the broken line b indicates the case the radial load F_(r) is ata middle level {F_(r)=3920 N (400 kgf) }, and the chain line c indicatesthe case the radial load F_(r) is at a small level {F_(r)=2940 N (300kgf)}.

As apparent from FIG. 8, even though the axial load F_(a) is identical,the ratio “n_(ca)/n_(i)” of the revolution speed n_(ca) to therotational speed n_(i) of the hub 2 becomes different when the preloadF₀ and the radial load F_(r) become different. In addition, when variousvehicle running stabilizing systems are to be controlled with highprecision, this ratio “n_(ca)/n_(i)” should not be ignored because anamount of deviation of this ratio caused due to variations of thepreload F₀ and the radial load F_(r) becomes considerably large. This istrue of the case that the axial load F_(a) is measured based on therevolution speed n_(cb) of the rolling elements 9 b, 9 b constitutingthe right side row in FIG. 4 that support the axial load F_(a).

In the case of the present embodiment, since the revolution speedsn_(ca), n_(cb) of the rolling elements 9 a, 9 b on a pair of rows,directions of the contact angles α_(a) , α_(b) of which are different(opposite) mutually, are sensed by a pair of revolution speed sensors 21a, 21 b respectively, the axial load F_(a) loaded to the rolling bearingunit is measured while suppressing the influence of variations in thepreload F₀ and the radial load F_(r) small. In other words, in the caseof the present embodiment, the revolution speeds n_(ca), n_(cb) of therolling elements 9 a, 9 b on apair of rows, magnitudes of the contactangles α_(a) , α_(b) of which are equal (in a state that no axial loadis applied) but directions of which are different mutually, are sensedby a pair of revolution speed sensors 21 a, 21 b, and then thecalculator (not shown) calculates the axial load F_(a) based on bothrevolution speeds n_(ca), n_(cb).

In this manner, any one method of following (1) to (4) is employed tosense the axial load F_(a) based on both revolution speeds n_(ca),n_(cb).

(1) The axial load F_(a) applied between the outer ring 1 and the hub 2is calculated based on the ratio “n_(cb)/n_(ca)” of the revolution speedn_(cb)of the rolling elements 9 b, 9 b in the other row to therevolution speed n_(ca) of rolling elements 9 a, 9 a in one row.

(2) The axial load F_(a) applied between the outer ring 1 and the hub 2is calculatedbasedon a dif ference “n_(cb)−n_(ca)” between therevolution speed n_(ca) of rolling elements 9 a, 9 a in one row and therevolution speed n_(cb) of the rolling elements 9 b, 9 b in the otherrow.

(3) The axial load F_(a) applied between the outer ring 1 and the hub 2is calculated based on a ratio “(n_(cb)−n_(ca))/n_(i)” of the difference“n_(cb)−n_(ca)” between the revolution speed n_(ca) of rolling elements9 a, 9 a in one row and the revolution speed n_(cb) of the rollingelements 9 b, 9 b in the other row to the rotational speed n_(i) of thehub 2.

(4) The axial load F_(a) applied between the outer ring 1 and the hub 2is calculated based on a synthesized signal obtained by synthesizing asignal representing the revolution speed n_(ca) of rolling elements 9 a,9 a in one row and a signal representing the revolution speed n_(cb) ofthe rolling elements 9 b, 9 b in the other row. The methods in (1) to(4) will be explained hereunder.

First, the above method in (1) will be explained with reference to FIG.9 hereunder. FIG. 9 shows a relationship between the ratio“n_(cb)/n_(ca)” of the revolution speed n_(cb) of the rolling elements 9b, 9 b in the other row to the revolution speed n_(ca) of the rollingelements 9 a, 9 a in one row and the axial load F_(a). A solid line a abroken line b, and a chain line c depicted in FIG. 9A, 9B respectivelyshow the relationship between the ratio “n_(cb)/n_(ca)” and the axialload F_(a) respectively. Also, FIG. 9A shows the influence of a value ofthe preload F₀ applied to the rolling elements 9 a, 9 b upon therelationship between a magnitude of the axial load F_(a) and the ratio“n_(cb)/n_(ca)”. In FIG. 9A, the solid line a indicates the case thepreload F₀ is small, the broken line b indicates the case the preload F₀is at a middle level, and the chain line c indicates the case thepreload F₀ is at a large level. While, FIG. 9B shows the influence ofthe value of the radial load F_(r) upon the relationship between themagnitude of the axial load F_(a) and the ratio “n_(cb)/n_(ca)”. In FIG.9B, the solid line a indicates the case the radial load F_(r) is large,the broken line b indicates the case the radial load F_(r) is at amiddle level, and the chain line c indicates the case the radial loadF_(r) is at a small level.

As indicated by the lines a, b, c shown in FIG. 9A, 9B, the ratio“n_(cb)/n_(ca)” of the revolution speed n_(cb) of the rolling elements 9b, 9 b in the other row to the revolution speed n_(ca) of the rollingelements 9 a, 9 a in one row is increased in compliance with an increaseof the axial load F_(a). Accordingly, if the relationship between theratio “n_(cb)/n_(ca)” and the axial load F_(a) is derived in advanceexperimentally or by the calculation and then is installed (stored) intoa microcomputer constituting the calculator, the axial load F_(a) can becalculated based on both revolution speeds n_(ca), n_(cb). In addition,as evident by the comparison between the lines a, b, c shown in FIG. 9A,9B, the influences of the preload F₀ and the radial load F_(r) upon therelationship between the ratio “n_(cb)/n_(ca)” and the axial load F_(a)are small.

More specifically, the preload F₀ is applied uniformly to the rollingelements 9 a, 9 b in both rows and also the radial load F_(r) is appliedsubstantially uniformly. Therefore, even though the preload F₀ and theradial load F_(r) are varied, such variation affects small thecalculated value of the axial load F_(a). In this case, as apparent fromFIG. 7, when the axial load F_(a) is increased, an extent to which therevolution speed n_(cb) of the rolling elements 9 b, 9 b on the loadside (the side on which the axial load F_(a) is supported) isaccelerated and an extent to which the revolution speed n_(ca) of therolling elements 9 b, 9 b on the counter load side (the side on whichthe axial load F_(a) is not supported) is decelerated are slightlydifferent (absolute values of inclination angles of two lines a, bdepicted in FIG. 7 are different) . Therefore, when the axial load F_(a)is increased, the preload F₀ and the radial load F_(r) have influencesupon the relationship between the ratio “n_(cb)/n_(ca)” and the axialload F_(a). However, as appreciated apparently by the comparison betweenabove FIG. 9 and FIG. 8, such influences are small and can be ignored inpractical use unless very precise control is required. In this case, ifthe axial load F_(a) is derived by the method in (1), the rotationalspeed sensor 15 b 15 and the rotational speed encoder 13 a may beomitted since the rotational speed n_(i) of the hub 2 is not used.

Next, the method in (2) will be explained with reference to FIG. 10Ahereunder. In this case, the axial load F_(a) applied between the outerring 1 and the hub 2 is calculated based on the difference“n_(cb)−n_(ca)” between the revolution speed n_(ca) of rolling elements9 a, 9 a in one row and the revolution speed n_(cb) of the rollingelements 9 b, 9 b in the other row. As apparent from the lines a, b inFIG. 7, the difference “n_(cb)“n_(ca)” between the revolution speedsn_(ca), n_(cb) is increased as the axial load F_(a) is increased. Also,both lines a, b are shifted in the vertical axis direction withvariations of the preload F₀ and the radial load F_(r), but such shiftappears almost equal in both lines a, b and in the same direction.Therefore, the influences of the preload F₀ and the radial load F_(r)upon the relationships between the difference “n_(cb)−n_(ca)” betweenthe revolution speeds n_(ca), n_(cb) and the axial load F_(a) are small.That is, even if the preload F₀ and the radial load F_(r) are varied,the influence of such variation upon the value of the axial load F_(a)derived based on the difference “n_(cb)−n_(ca)” between the revolutionspeeds n_(ca), n_(cb) is suppressed small.

Therefore, as indicated by a solid line d in FIG. 10A, if therelationship between the difference “n_(cb)−n_(ca)” between therevolution speeds n_(ca), n_(cb) and the axial load F_(a) is derived inadvance experimentally or by the calculation and then is installed intothe microcomputer constituting the calculator, the axial load F_(a) canbe calculated based on the difference “n_(cb)−n_(ca)” between bothrevolution speeds n_(ca), n_(cb). In addition, the axial load F_(a) canbe sensed precisely while suppressing the influence of the variation ofthe preload F₀ and the radial load F_(r). In this manner, if the axialload F_(a) is derived by the method in (2), the rotational speed sensor15 b and the rotational speed encoder 13 a may be omitted since therotational speed n_(i) of the hub 2 is not used.

Next, the method in (3) will be explained with reference to FIG. 10Bhereunder. In this case, the difference “n_(cb)−n_(ca)” between therevolution speed n_(ca) of the rolling elements 9 a, 9 a in one row andthe revolution speed n_(cb) of the rolling elements 9 b, 9 b in theother row is sensed, and then the ratio “(n_(cb)−n_(ca))/n_(i)” of thedifference “n_(cb)−n_(ca)” to the rotational speed n_(i) of the hub 2 iscalculated. Then, the axial load F_(a) applied between the outer ring 1and the hub 2 is calculated based on this ratio “(n_(cb)−n_(ca))/n_(i)”.In this case, as indicated by a solid line e in FIG. 10B, if therelationship between the ratio “(n_(cb)−n_(ca))/n_(i)” and the axialload F_(a) is derived in advance experimentally or by the calculationand then is installed into the microcomputer constituting thecalculator, the axial load F_(a) can be calculated based on thedifference “n_(cd)−n_(ca)” between both revolution speeds n_(ca),n_(cb). In addition, the axial load F_(a) can be detected exactlyirrespective of change in the rotational speed of the hub 2 withsuppressing the influence of the variations of the preload F₀ and theradial load F_(r).

If the rolling bearing unit is used in the condition that the rotationalspeed of the rotating ring is always kept constant, like the rotationsupporting portion of the machine tool or the carrier vehicle in thefactory, the axial load F_(a) can be detected exactly only by thedifference “n_(cb)−n_(ca)” between the revolution speeds n_(ca), n_(cb)of the rolling elements 9 a, 9 b in both rows, like the above method in(2). On the contrary, if the rotational speed of the rotating ring (hub2) is changed in operation, like the rolling bearing unit used tosupport the wheel of the car or the railway vehicle, the difference“n_(cb)−n_(ca)” between the revolution speeds n_(ca), n_(cb) is changedin response to this rotational speed regardless of the axial load F_(a).Consequently, in such case, like the above method in (3), if the axialload F_(a) is calculated based on the rotational speed n_(i) of the hub2 sensed by the rotational speed sensor 15 b and the difference“n_(cb)−n_(ca)” between the revolution speeds n_(ca), n_(cb) theinfluence of the rotational speed n_(i) of the hub 2 can be eliminated.

Further, the above method in (4) will be explained with reference toFIGS. 11 to 16 hereunder. In this case, the calculator gets asynthesized signal by synthesizing (superposing) a signal representingthe revolution speed n_(ca) of the rolling elements 9 a, 9 a in one row,which is fed from the revolution speed sensor 21 a, and a signalrepresenting the revolution speed n_(cb) of the rolling elements 9 b, 9b in the other row, which is fed from the revolution speed sensor 21 b.Then, the axial load F_(a) applied between the outer ring 1 and the hub2 is calculated based on the synthesized signal. The method in (4)synthesizes in advance the signals sent out from the revolution speedsensors 21 a, 21 b, and thus makes it possible to shorten a full lengthof a harness and reduce an amount of computation in the calculator.

Like above FIG. 7, FIG. 11 is a diagram showing a relationship betweenthe axial load F_(a) and a magnitude of the preload F₀, in addition tothe relationship between the axial load F_(a) and the ratio of therevolution speeds of the rolling elements 9 a, 9 b in both rows to therotational speed of the hub 2. In above FIG. 11, the numerical value onthe axis of ordinate is increased upwardly conversely to above FIGS. 7and 8. Also, like above FIG. 10B, FIG. 12 is a diagram showingrelationships among a ratio of a difference in the revolution speeds ofthe rolling elements 9 a, 9 b in a pair of rows to the rotational speedof the hub 2, a magnitude of the axial load F_(a), and a magnitude ofthe preload F₀. As apparent from FIGS. 11 and 12, the revolution speedsn_(ca), n_(cb) of the rolling elements 9 a, 9 b in both rows are changedin the opposite direction in answer to the axial load F_(a) and also areaccelerated as the preload F₀ is increased. Like the above method in(3), the above method in (4) calculates the axial load F_(a) appliedbetween the outer ring 1 and the hub 2, based on the ratio“(n_(cd)−n_(ca))/n_(i)” of the difference “n_(cb)−n_(ca)” between therevolution speeds n_(ca), n_(cb) of the rolling elements 9 a, 9 b in apair of rows to the rotational speed n_(i) of the hub 2 by utilizing therelationship in FIG. 12.

In particular, in the case of the method in (4), the synthesized signalis derived by the calculator to synthesize the signals representing therevolution speeds n_(ca), n_(cb) of the rolling elements 9 a, 9 b inboth rows, which are sent out from a pair of revolution speed sensors 21a, 21 b. Then, the axial load F_(a) is calculated based on thesynthesized signal and the rotational speed n_(i) of the hub 2. Themethod of processing the synthesized signal in this case is slightlydifferent in the case that the signals sent out from the revolutionspeed sensors 21 a, 21 b are changed like a sine wave and the case thatthe signals are changed like a pulse wave.

First, the case that the signals are changed like a sine wave will beexplained with reference to FIGS. 13 and 14 hereunder. In this case, asynthesized signal shown in FIG. 14B is obtained by synthesizing(superposing) the signals sent out from the revolution speed sensors 21a, 21 b and shown in FIG. 14A respectively. This synthesized signal hasa swell having a swell period T₁. This swell is generated by adifference between the signals fed from the revolution speed sensors 21a, 21 b, and a reciprocal (1/T₁frequency) of the swell period T₁gives adifference in frequencies of the signals sent out from the revolutionspeed sensors 21 a, 21 b. Therefore, the difference “n_(cb)−n_(ca)”between the revolution speeds n_(ca), n_(cb) of the rolling elements 9a, 9 b in both rows is calculated by the swell period T₁ or thefrequency, and then the axial load F_(a) applied between the outer ring1 and the hub 2 is calculated based on the ratio “(n_(cd)−n_(ca))/n_(i)”of the difference “n_(cb)−n_(ca)” to the rotational speed n_(i) of thehub 2.

The synthesis (superposition) of the signals sent out from therevolution speed sensors 21 a, 21 b can be carried out by a simplecircuit, and also only one harness for supplying the synthesized signalis required. Also, the calculation of the revolution speeds n_(ca),n_(cb) every rolling elements 9 a, 9 b in both rows is not required ofthe calculator that receives the synthesized signal. That is, thedifference between the revolution speeds n_(ca), n_(cb) can be senseddirectly. For this reason, as described above, reduction in the fulllength of the harness and reduction in an amount of computation in thecalculator portion can be achieved.

Next, the case that the signals are changed like a pulse wave will beexplained with reference to FIGS. 15 and 16 hereunder. In this case, asynthesized signal shown in FIG. 16B is obtained by synthesizing(superposing) the signals sent out from the revolution speed sensors 21a, 21 b and shown in FIG. 16A respectively. This synthesized signal ischanged by a period T₂. This change (change in a pulse width) isgenerated by a difference between the signals fed from the revolutionspeed sensors 21 a, 21 b, and a reciprocal (1/T₂, frequency) of thechange period T₂ gives a difference in frequencies of the signals sentout from the revolution speed sensors 21 a, 21 b.

Therefore, the difference “n_(cd)−n_(ca)” between the revolution speedsn_(ca), n_(cb) of the rolling elements 9 a, 9 b in both rows iscalculated by the change period T₂ or the frequency, and then the axialload F_(a) applied between the outer ring 1 and the hub 2 is calculatedbased on the ratio “(n_(cb)−n_(ca))/n_(i)” of the difference“n_(cb)−n_(ca) to the rotational speed n_(i) of the hub 2. This case issimilar to the case that the signals are changed like a sine wave,except that the swell period T₁ is replaced with the change periodT_(z).

Second Embodiment

FIG. 17 shows a second embodiment of the present invention. In thepresent embodiment, even though the revolution speed encoder 26 a (alsothe revolution speed encoder 26 b shown in FIGS. 1 and 2) iseccentrically moved, the revolution speeds of the rolling elements canbe sensed precisely by providing a plurality of revolution speed sensors21 a ₁, 21 a ₂ (two in FIG. 17). Therefore, in the case of the presentembodiment, the revolution speed sensors 21 a ₁, 21 a ₂ are arranged todeviate from the revolution direction of the rolling elements 9 a, 9 b(see FIG. 1) whose revolution speeds are to be sensed. Moreparticularly, the revolution speed sensors 21 a ₁, 21 a ₂ are arrangedin opposite positions with respect to a rotation center O₂ of the hub 2(see FIG. 1) by 180 degree. Then, the present embodiment is constructedto eliminate the influence of an error caused by the eccentric motion ofthe revolution speed encoder 26 a by adding the sensed signals of therevolution speed sensors 21 a ₁, 21 a ₂. This respect will be explainedwith reference to FIGS. 18 to 20 in addition to FIG. 17.

A clearance required to hold rotatably these rolling elements 9 a, 9 bis provided between an inner surface of a pocket of the retainer 22 a,in which the revolution speed encoder 26 a is held (or the retaineritself has a function as the encoder), and the rolling contact surfacesof the rolling elements 9 a, 9 b. Therefore, no matter how an assemblingprecision of respective constituent members is enhanced highly, it ispossible that a rotation center O₂₂ of the retainer 22 a is deviatedfrom a center O₂ of a pitch circle of the rolling elements 9 a, 9 b(rotation center of the hub 2) by δ in operation of the rolling bearingunit, as shown exaggeratingly in FIGS. 17, 19. Then, the revolutionspeed encoder 26 a performs a whirling motion around.the rotation centerO₂₂ based on this deviation. As the result of this whirling motion, asensed surface of the revolution speed encoder 26 a has a movingvelocity except the rotation direction. Then, this moving velocityexcept the rotation direction, e.g., a moving velocity in the lateraldirection in FIGS. 17 and 19, is added/subtracted to/from the movingvelocity in the rotation direction. In contrast, since the revolutionspeed sensors sense the revolution speeds of the rolling elements 9 a, 9b based on the moving velocity of the sensed surface of the revolutionspeed encoder 26 a, an eccentricity affects the sensed signal of therevolution speed sensor, the sensing surface of which is opposed to aside surface of the revolution speed encoder 26 a .

For instance, as shown in FIG. 19, in case only one sensing surface ofone revolution speed sensor 21 a, is opposed to the side surface of therevolution speed encoder 26 a, the sensed signal of the revolution speedsensor 21 a, is changed, as shown in FIG. 20. In other words, even whenthe revolution speeds of the rolling elements 9 a, 9 b are constant asindicated by a solid line α, the revolution speed represented by theoutput signal of the revolution speed sensor 21 a, is changed like asine wave, as indicated by a broken line β. More particularly, in casethe moving velocity in the horizontal direction in FIG. 19 is added tothe moving velocity in the rotation direction, the output signal gives asignal that corresponds to the velocity that is quicker than the actualrevolution speed. Conversely, in case the moving velocity in thehorizontal direction in FIG. 19 is subtracted from the moving velocityin the rotation direction, the output signal gives a signal thatcorresponds to the velocity that is slower than the actual revolutionspeed. FIG. 19 depicts an eccentricity in an exaggerated fashion ratherthan the actual case. In this event, in case the loads applied to therolling bearing unit (the radial load F_(r) and the axial load F_(a)must be sensed more precisely to execute the control of the vehiclestability more strictly, there is such a possibility that an errorcaused by the eccentricity becomes a problem.

In contrast, in the case of the present embodiment, apair of revolutionspeed sensors 21 a ₁, 21 a ₂ are provided. Therefore, as shown in FIG.17, in case a rotation center O₂₂ of the retainer 22 a is deviated fromthe center of a pitch circle of the rolling elements 9 a, 9 b (rotationcenter of the hub 2), in other words, in case the retainer 22 a performsa whirling motion due to an eccentricity, the revolution speed of therolling elements 9 a, 9 b can be sensed precisely. That is, therevolution speed sensors 21 a ₁, 21 a ₂ arranged in the oppositepositions by 180 degree with respect to a center O₂ of the pitch circleare affected in the reverse direction by the same amount.

More concretely, as shown in FIG. 18, in case the revolution speedof therolling elements 9 a, 9 b is constant as indicated by a solid line α,the revolution speed represented by the output signal of one revolutionspeed sensor 21 a ₁ is changed like a sine wave, as indicated by abroken line β, whereas the revolution speed represented by the outputsignal of the other revolution speed sensor 21 a ₂ is also changed likea sine wave, as indicated by a chain line γ. In this case, a changingperiod of the revolution speed represented by the output signal of onerevolution speed sensor 21 a ₁ and a changing period of the revolutionspeed represented by the output signal of the other revolution speedsensor 21 a ₂ are shifted by almost 180 degree mutually. Therefore, ifthe speeds derived from the output signals of a pair of revolution speedsensors 21 a ₁, 21 a ₂ are added (a sum is calculated) and then dividedby 2, the revolution speed of the rolling elements 9 a, 9 b can bemeasured precisely independent of the whirling motion generated due tothe eccentricity. Also, in order to execute the control of the vehiclestability more strictly, the load applied to the rolling bearing unitcan be sensed precisely.

In this case, the technology to correct the error generated by theeccentric motion of the retainer by arranging a plurality of revolutionspeed sensors in equal interval positions in the circumferentialdirection of the revolution direction of the rolling elements (in theillustrated example, in the opposite positions by 180 degree) can beapplied to any bearing unit as well as the double row rolling bearingunit used to support the wheels, as shown in FIG. 1. For example, asshown in FIG. 21, such technology can be applied to a single row deepgroove or angular contact ball bearing. In such ball bearing, aplurality of rolling elements 9, 9 are provided between an outer ringraceway 29 and an inner ring raceway 30, which are formed on mutuallyopposing peripheral surfaces of an outer ring 27 and an inner ring 28arranged in a concentric fashion respectively, and is used in a statethat the contact angles and the enough preload are applied (in a statethat the preload is never lost in operation) In the example shown inFIG. 21, sensing surfaces of a pair of revolution speed sensors 21 a ₁,21 a ₂ fitted to a cover 31, which is fitted/fixed to an outer peripheryof the outer ring 27, are opposed to a side surface of a revolutionspeed encoders 26 coupled to a retainer 22 in the opposite positionswith respect to arotation center of the inner ring 28 by 180 degree.

In this case, if the rolling bearing unit, in which the rolling elementsare provided in double rows and to which the present invention isapplied, is used in a state that the rotational speed of the rotatingring is always constant like the rotation supporting portion of themachine tool or the carrier car in the factory, the radial load F_(r)can be detected exactly by using only a Sum “n_(cb)+n_(ca)” or a product“n_(ca)×n_(cb)” of the revolution speeds n_(ca), n_(cb) of the rollingelements 9 a, 9 b in both rows. Also, the axial load F_(a) can bedetected exactly by using only the difference “n_(cd)−n_(ca)” of therevolution speeds. On the contrary, if the rotational speed of therotating ring is changed in operation like the rolling bearing unit usedto supporting the wheels of the car or the railway vehicle, the sum“n_(cb)+n_(ca)” or the product “n_(ca)×n_(cb)” or the difference“n_(cb)−n_(ca)” of the revolution speeds n_(ca), n_(cb) is changed inresponse to the rotational speed irrespective of the radial load F_(r)and the axial load F_(a). For this reason, in such case, as describedabove, the influence of the rotational speed n_(i) of the hub 2 can beeliminated since the radial load F_(r) or the axial load F_(a) ismeasured based on the rotational speed n_(i) of the hub 2 sensed by therotational speed sensor 15 b and the revolution speeds n_(ca), n_(cb).

In this case, even when the radial load F_(r) or the axial load F_(a) ismeasured by any method, the inexpensive speed sensors used widely to getthe control signal of the ABS or the TCS in the related art can be usedas the revolution speed sensors 21 a, 21 b used to measure therevolution speeds n_(ca), n_(cb) of the rolling elements 9 a, 9 b indouble rows and the rotational speed sensor 15 b used to measure therotational speed of the hub 2. As a result, the overall load measuringsystem for the rolling bearing unit can be constructed inexpensively.

Third Embodiment

In the illustrated example, the case that the revolution speeds of therolling elements 9 a, 9 b in double rows are measured as the rotationalspeeds of the retainers 22 a, 22 b holding the rolling elements 9 a, 9 bin double rows is explained. But the revolution speeds of the rollingelements 9 a, 9 b in double rows can be measured directly. For example,if the magnetic sensors are used as the revolution speed sensors 21 a,21 b and the elements made of magnetic material is used as the rollingelements 9 a, 9 b in double rows, characteristics of the magneticsensors constituting the revolution speed sensors 21 a, 21 b arechangedwith the revolution of the rolling elements 9 a, 9 b in doublerows (in the case of the active sensor into which the magnetic sensorsare incorporated). In other words, a quantity of magnetic flux flowingthrough the magnetic sensors is increased at an instance when therolling elements 9 a, 9 b made of magnetic material are present invicinity of the sensing surfaces of the revolution speed sensors 21 a,21 b, while a quantity of magnetic flux flowing through the magneticsensors is reduced at an instance when the sensing surfaces are opposedto adjacent portions located between the rolling elements 9 a, 9 b inthe circumferential direction. In this way, a frequency at which thecharacteristics of the magnetic sensors are changed in answer to thechange in the quantity of magnetic flux flowing through the magneticsensors is proportional to the revolution speed of the rolling elements9 a, 9 b in double rows. As a result, the revolution speed can bederived based on the sensed signals of the revolution speed sensors 21a, 21 b into which the magnetic sensors are incorporated.

In this case, in order to sense the revolution speed of the rollingelements 9 a, 9 b in double rows by the above mechanism, the rollingelements 9 a, 9 b in double rows must be made of the magnetic material.Therefore, when the elements made of non-magnetic material such asceramics, or the like are used as the rolling elements 9 a, 9 b indouble rows, optical sensors must be used as the revolution speedsensors 21 a, 21 b. However, in many cases a grease to lubricate therolling contact portions is sealed in a space 32 into which the sensingportions of the revolution speed sensors 21 a, 21 b are inserted (seeFIGS. 1 and 2), and thus the light is not effectively reflected in suchcases. With regard to above circumstances, it is preferable that theelements made of magnetic material shouldbe used as the rolling elements9 a, 9 b in double rows and also the sensors into which the magneticsensors are incorporated should be used as the revolution speed sensors21 a, 21 b.

Also, as described above, it is preferable that, when the revolutionspeed of the rolling elements 9 a, 9 b in double rows is directlymeasured by the revolution speed sensors 21 a, 21 b, the retainers madeof non-magnetic material such as synthetic resin, or the like should beused as the retainers 22 a, 22 b to hold the rolling elements 9 a, 9 bin double rows. If the retainers made of magnetic material are used, themagnetic fluxes to be flow between the rolling elements 9 a, 9 b indouble rows and the sensing portions of the revolution speed sensors 21a, 21 b are cut off, and thus it is impossible to measure the exactrevolution speed. Conversely speaking, the revolution speed of therolling elements 9 a, 9 b in double rows can be measured exactly byusing the retainers 22 a, 22 b made of non-magnetic material. In thiscase, the retainers 22 a, 22 b may be made of non-magnetic metal such ascopper alloy, or the like, but more preferably the retainers made ofsynthetic resin should be employed because such retainers are light inweight and are difficult to cut off the magnetic fluxes. For example,because the austenite-based stainless steel that is normally known asthe non-magnetic metal has also minute magnetism, such steel isdisadvantageous to sense exactly the revolution speed.

If the structure in which the ceramic elements are used as the rollingelements 9 a, 9 b in double rows and the revolution speeds n_(ca),n_(cb) of the rolling elements 9 a, 9 b in double rows are measured asthe rotational speeds of the retainers 22 a, 22 b is employed, it isadvantageous tomeasure exactlythe revolution speeds n_(ca), nob In otherwords, the ceramics is lighter in weight than the hard metal such asbearing steel, the stainless steel, or the like, which is normallyutilized to construct the rolling elements 9 a, 9 b , and has a smallercentrifugal force as well as a smaller inertial mass both acting inoperation. Hence, since a contact pressure on contact portions betweenrolling contact surfaces of the rolling elements 9 a, 9 b and the outerring raceways 7, 7 is lowered and the inertialmass becomes small, thefollow-upperformance to sudden change in the speed can be improved.Also, even when the speed of the hub 2 is suddenly changed, a slip(revolution slip) is difficult to occur on the contact portions betweenthe rolling contact surfaces of the rolling elements 9 a, 9 b and theouter ring raceways 7, 7 and the inner ring raceways 8, 8.

In other words, the revolution speeds n_(ca), n_(cb) of the rollingelements 9 a, 9 b in double rows are changed exactly to correspond tothe change in the rotational speed n₁ of the hub 2. Hence, even when therotational speed n_(i) of the hub 2 is suddenly changed, the radial loadF_(r) and the axial load F_(a) applied to the rolling bearing unit canbe measured exactly based on the rotational speed n_(i) and therevolution speeds n_(ca), n_(cb). In this case, the technology tomeasure exactly the revolution speed of the rolling elements whilesuppressing the revolution slip by forming the rolling elements of theceramics in this way can be applied to not only the case that therolling elements are formed of elements except the balls but also thecase of the single row rolling bearing unit instead of the double rowtype.

Also, as the revolution speed sensors 21 a, 21 b and the rotationalspeed sensor 15 b, the passive magnetic revolution sensor in which acoil is wound around a pole piece made of magnetic material can be used.In this case, a voltage of the sensed signal of the passive magneticrevolution sensor is lowered when the rotational speed becomes slow. Inthe case of the load measuring device for the rolling bearing unit asthe object of the present invention, because such device intends toimplement the running stability during the high-speed running of themobile body as a major object, reduction of the voltage of the sensedsignal during the low-speed running is hard to become an issue.Accordingly, if the inexpensive passive sensor is employed as one orplural sensors out of respective sensors 21 a, 21 b, 15 b, reduction ina cost of the overall device can be achieved. In this case, it ispreferable that, if a high-precision control during the low-speedrunning is also intended, the active revolution sensor into which themagnetic sensors are incorporated should be used as described above.

Also, it is preferable that, in case either the active sensor is used asthe revolution sensor or the passive sensor is used, the magnetismsensing element such as Hall element, etc. and sensor constituent partssuch as permanent magnet, yoke (pole piece), coil, etc. should be moldedin a holder made of non-magnetic material such as synthetic resin, orthe like except the sensing surfaces at the top end portion. In thismanner, the sensing portions of the revolution sensor constructed bymolding the sensor constituent parts in the synthetic resin are opposedto the sensed portions, i.e., of the revolution speed encoders 26 a, 26b fitted to the rolling elements 9 a, 9 b in double rows or theretainers 22 a, 22 b in the case of the revolution speed sensors 21 a,21 b or the rotational speed encoder 13 a in the case of the rotationalspeed sensor 15 b, respectively. In this fashion, the above sensors 21a, 21 b, 15 b are held in one holder, the operation of fitting thesesensors 21 a, 21 b, 15 b into the outer ring 1 can be facilitated. Inthis case, these sensors 21 a, 21 b, 15 b may be fitted separately tonon-rotated portions according to the applications.

Also, the signals sensed by the revolution speed sensors 21 a, 21 b torepresent the revolution speed of the rolling elements 9 a, 9 b indouble rows and the signal sensed by the rotational speed sensor 15 b torepresent the rotational speed of the hub 2 may be processed by thehardware such as analog circuit, or the like or the software using themicrocomputer, or the like. Also, in the illustrated example, the casethat the present invention is applied to the double row angular contactrolling bearing unit used to support the wheel of the vehicle isexplained. But the present invention may be applied to the normal doublerow or multiple row ball bearing or tapered roller bearing. In thiscase, when the present invention is applied to the multiple row (threerows or more) rolling bearing, the loads applied to the rolling bearingunit are calculated by sensing the revolution speed in remaining rows inaddition to the revolution speed of the rolling elements in two rows.Also, when the present invention is applied to the double row taperedroller bearing in which tapered rollers are used as the rollingelements, an amount of change in the revolution speed becomes smallerthan the double row ball bearing, nevertheless the load can becalculated based on change in the revolution speed of the taperedrollers.

Further, even when the present invention is applied to the double rowangular contact rolling bearing unit used to support the wheel of thevehicle, the present invention can be implemented in any hub unit aswell as so-called third-generation hub unit in which the outside innerring raceway 8 is formed on the outer peripheral surface of the hub mainbody 4 in the middle portion, as shown in FIG. 1. In other words, thepresent invention may be applied to the so-called second-generation hubunit, in which a pair of inner rings are fitted/fixed to the middleportion or the inner end portion of the hub main body, and the so-calledfirst-generation hub unit, in which a pair of inner rings arefitted/fixed to the middle portion or the inner end portion of the hubmain body and also the outer ring whose outer periphery is shaped into amere cylinder is inserted/supported into the supporting hole of theknuckle. Alternately, like the structure shown in FIG. 21, the presentinvention may be applied to the structure in which a pair of rollingbearings each serving as the single row rolling bearing respectively areprovided between an outer peripheral surface of the hub main body in themiddle portion or the inner end portion and an inner peripheral surfaceof the supporting hole of the knuckle to construct the double rowrolling bearing unit. Of course, the application of the presentinvention is not limited to the hub unit for the idler wheel as shown,and the present invention may be applied to the hub unit for the drivingwheel (rear wheels of FR car, RR car, MR car, front wheels of FF car,and all wheels of 4WD car), as shown in above FIGS. 38 to 40.

Fourth Embodiment

Moreover, as described above, when the present invention is implemented,the revolution speeds n_(ca), n_(cb) of the rolling elements 9 a, 9 b indouble rows are measured in the course of measuring the radial loadF_(r) and the axial load F_(a). Then, if these revolution speeds n_(ca),n_(cb) in respective rows are detected, the contact angles α(α_(a),α_(b)) can be calculated based on above Eq. (1). Therefore, if thecontact angles a are monitored, an alarm unit for generating an alarm atthe time of abnormal state by grasping the state of the rolling bearingunit can be constructed. As the time of abnormal state, the case thepreload to the rolling bearing unit is lost (the preload escapementoccurs) , the case the excessive axial load F_(a) is loaded to therolling bearing unit, etc. may be considered, for example. In the casethat the preload out of them is lost, contact angles α become small.Then, vibrations or noises caused due to the shake are generated, and inaddition wears of the rolling contact surfaces of the rolling elements 9a, 9 b in double rows and the outer ring raceway 7 and the inner ringraceway 8 are advanced because of the revolution slip. In contrast, incase the excessive axial load F_(a) is applied, the contact angle α inany row is increased. Also, not only the contact pressure of the contactportions between the rolling contact surfaces of the rolling elements 9a (9 b) in the concerned row and the outer ring raceway 7 and the innerring raceway 8 is increased excessively to increase the rotationalresistance of the rolling bearing unit, but also it is possible that apart of the rolling contact surfaces is off the outer ring raceway 7 andthe inner ring raceway 8 in the most remarkable case. In any case, therolling contact fatigue life of respective surfaces is lowered becauseof the exfoliation caused on respective surfaces, etc.

All the states that the preload escapement is generated or the excessiveaxial load F_(a) is loaded to cause such problem can be grasped bymonitoring the contact angles α. Therefore, the contact angles α of therolling elements 9 a, 9 b in each row are compared with the normal valueby the circuit shown in the FIG. 22 while monitoring them, the alarmingdevice for generating an alarm when deviation from the normal valuebecomes large can be constructed. When such alarming device isconstructed, a lifetime of the rolling bearing unit can be predicted orthe event that generation of a serious trouble in the machine devicesuch as the car, the machine tool, the industrial equipment, etc., intowhich such rolling bearingunit is incorporated,canbepreventedpreviously. As the alarm in this case, lightening of analarm lamp, start of the alarming device such as a buzzer, or the likemay be considered.

The circuit shown in FIG. 22 is constructed to generate the alarm aboutthe concerned row by monitoring the contact angles α_(a), α_(b) of therolling elements 9 a, 9 b in double rows respectively when the contactangles α_(a), α_(b) of the rolling elements 9 a, 9 b in any one row aredeviated from the normal value by a predetermined value or more. Forthis reason, the rotational speed n_(i) of the hub 2 being fed from therotational speed sensor 15 b, the revolution speed n_(ca), n_(cb) of therolling elements 9 a, 9 b in double rows being fed from the revolutionspeed sensors 21 a, 21 b, and specifications of the rolling bearing unitbeing stored in a memory 34 are input into an arithmetic circuit 33.Various values necessary for calculation of the contact angles α_(a),α_(b) of the rolling elements 9 a, 9 b in respective rows such as apitch circle diameter D of the rolling elements 9 a, 9 b in double rows,a diameter d of these rolling elements 9 a, 9 b, etc. as well as aninitial contact angle α_(o) of the rolling elements 9 a, 9 b inrespective rows are stored in the memory 34 by inputting the modelnumber of the rolling bearing unit or inputting directly the necessaryvalues.

The arithmetic circuit 33 calculates the contact angles α_(a), α_(b) ofthe rolling elements 9 a, 9 b in respective rows based on respectivespeed nj, n_(ca), n_(cb)and respective diameters D, d, and then feedsthem to comparators 35 a, 35 b. These comparators 35 a, 35 b compare thecontact angles α_(a), α_(b) of the rolling elements 9 a, 9 b inrespective rows with the initial contact angle α_(o) fed from the memory34 at a time point of calculation. Then, it is decided whether or notthe contact. angles α_(a), α_(b) of the rolling elements 9 a, 9 b inrespective rows are within the normal range. If it is decided that suchcontact angles α_(a), α_(b) are out of the normal range (abnormal),alarms 36 a, 36 b are caused to generate the alarm.

The approach to decide whether or not the operation state of the rollingbearing unit is proper is not limited to the step of comparing thecontact angles α_(a), α_(b) of the rolling elements 9 a, 9 b inrespective rows with the initial contact angle α_(o). Any approach maybe carried out. For example, it is possible to decide whether or not theoperation state of the rolling bearing unit is proper, by detecting anelastic deformation amount δ, the radial load F_(r), the axial loadF_(a), and contact stiffness K of the rolling bearing unit and thencomparing them with the specifications of the rolling bearing unit. Inthis case, the arithmetic circuit 33 executes calculations given by Eqs.(2) to (5)(r _(i) +r _(e) −d)·cos α _(n)=(r _(i) +r _(e) +δ−d)·cos α _(o)   (2)where

-   -   ri: groove radius of the inner ring raceway (radius of curvature        of a sectional shape),    -   re: groove radius of the outer ring raceway (radius of curvature        of a sectional shape),    -   δ: elastic deformation amount,    -   α_(o): initial contact angle, and    -   α_(n): the contact angles (α_(a), α_(b)) in double rows in        operation,        Q=K _(N)×δ^(3/2)   (3)        where    -   Q: load of the rolling elements, and    -   K_(N): constant of the rolling elements,        F _(a) =z×Q×sinα _(n)   (4)        F _(r) =z×Q×cos α _(n)   (5)        where    -   z: number of the rolling elements.

Fifth Embodiment

FIG. 23 shows a fifth embodiment of the present invention. In the caseof the present embodiment, out of three sensors 21 a, 21 b, 15 binstalled onto the top end portion 24 of the sensor unit 23, onerotational speed sensor 15 b is positioned closer to the outerperipheral surface of the hub 2 than a pair of revolution speed sensors21 a, 21 b. When constructed in this manner, three sensors 21 a, 21 b,15 b are separated mutually and the magnetic interference among thesesensors 21 a, 21 b, 15 b is reduced. Since such magnetic interference issuppressed small, improvement in the reliability of sensing therevolution speed and the rotational speed and in turn the reliability ofcalculation of the load can be achieved.

Sixth Embodiment

FIG. 24 shows an sixth embodiment of the present invention. In the caseof the present embodiment, positions of three sensors 21 a, 21 b, 15 bprovided to the top end portion 24 of the sensor unit 23 are shiftedmore largely than the case of above fifth embodiment. More particularly,in the case of the present embodiment, the sensors 21 a, 21 b, 15 bpackaged in the IC package are aligned closer mutually in series withthe axial direction of the sensor unit 23. By doing this, the magneticinterference among these sensors 21 a, 21 b, 15 b is suppressed smallerand also a diameter of the sensor unit 23 is made small. Then, eventhough an interval between a pair of retainers 22 a, 22 b is set narrow,an inner diameter of the fitting hole 10 a (see FIGS. 1 and 2) formed inthe outer ring 1 such that the top end portion 24 of the sensor unit 23can be arranged therein and the sensor unit 23 is installed therein isformed small. Thus, improvement in the strength and the stiffness of theouter ring 1 is intended.

Seventh Embodiment

FIG. 25 shows an seventh embodiment of the present invention. In thecase of the present embodiment, a connector 37 is provided on the outerperipheral surface of the outer ring 1, and a plug 39 provided to oneend portion of a harness 38 used to output the sensed signals of thesensors 21 a, 21 b, 15 b can be connected to this connector 37. Theother end of the harness 38 is coupled to a controller provided to thevehicle body. In the case of the present embodiment, when the rollingbearing unit on which the sensor unit 23 equipped with respectivesensors 21 a, 21 b, 15 b is mounted previously is fitted to thesuspension system, damage of the harness 38 can be prevented byemploying such structure.

In more detail, as shown in FIG. 26, if a sensor unit 23′ equipped withrespective sensors 21 a, 21 b, 15 b and the harness 38 are combinedunseparably with each other, it is possible to damage the harness 38 inthe assembling operation. Also, the transporting operation (the packingoperation and the unpacking operation before such operation) of the loadmeasuring rolling bearing unit becomes troublesome. In contrast, in thecase of the present embodiment, since the assembling operation iscarried out in a state that the harness 38 is removed and then theharness 38 is coupled, the harness 38 is never damaged (an insulatingfilm is damaged, a conductor is disconnected, or the like) in theassembling operation. Also, the transporting operation of the loadmeasuring rolling bearing unit is made easy. In addition, when theharness 38 is damaged by a stone let fly during vehicle running, or thelike, an expense required for the repair can be reduced because only theharness 38 and the plug 39 should be exchanged.

In this case, the connector 37 provided to the outer ring 1 side may beprovided separately from the sensor unit 23, as show in FIG. 25, andalso may be provided integrally with a sensor unit 23 a, as show in FIG.27.

Eighth Embodiment

FIG. 28 shows an eighth embodiment of the present invention. In the caseof thepresent embodiment, an inner diameter a of the revolution speedencoder 26 a (26 b) attached to the side surface of the rim portion 25of the retainer 22 a (22 b) is set larger than an inner diameter A ofthe side surface of the rim portion 25, while an outer diameter b of thesame revolution speed encoder 26 a (26 b) is set smaller than an outerdiameter B of the side surface of the rim portion 25 (A<a<b<B). Sincedimensions of respective portions are defined in this manner, such anevent can be prevented that the revolution speed encoder 26 a (26 b)comes into contact with the inner peripheral surface of the outer ring 1and the outer peripheral surface of the hub 2 (see FIGS. 1 and 2, forexample).

Ninth Embodiment

FIGS. 29 and 30 shows a ninth embodiment of the present invention. Inthe case of the present embodiment, a rotational speed encoder 13b usedto sense the rotational speed of the hub 2 and the rotational speedsensor 15 b are provided to the inner end portion of the rolling bearingunit. Only the revolution speed encoders 26 a, 26 b and the revolutionspeed sensors 21 a, 21 b are provided between the rolling elements 9 a,9 b aligned in two rows. In the case of the present embodiment, byemploying such structure, even when an interval between the rows of therolling elements 9 a, 9 b is narrow, it can be prevented that themagnetic interference is caused by excessively close arrangement ofrespective sensors 21 a, 21 b, 15 b, and also it can be prevented thatthe diameter of the sensor unit 23 is increased to such an extent thatsuch diameter cannot be inserted into a space between the rows of therolling elements 9 a, 9 b. In addition, since the inner diameter of thefitting hole 10 a used to insert the sensor unit 23 is reduced,improvement in the strength and the stiffness of the outer ring 1 ismade easy.

In this case, the rotational speed encoder 13 b may be fitted/fixedindependently to the inner end portion of the hub 2, as shown in FIG.29, or may be attached to a side surface of a slinger 40 constituting acombination sealing ring, as shown in FIG. 30. Also, the rotationalspeed sensor 15 b may be fitted/fixed to the cover 14 that is put on theopening portion at the inner end of the outer ring 1, as shown in FIG.29, or may be fitted/fixed directly to the outer ring 1, as shown inFIG. 30. Like the case of above respective embodiments, the gear such asthe permanent magnet, the magnetic material, or the like may be used asrespective encoders 13 b, 26 a, 26 b, the magnetic sensor such as theactive type, the passive type, or the like may be used as respectivesensors 21 a, 21 b, 15 b, the calculator used to calculate the load maybe provided to the rolling bearing unit or may be provided separatelyfrom the rolling bearing unit, and so forth.

Tenth Embodiment

FIG. 31 shows a tenth embodiment of the present invention. As describedabove, if the revolution speed encoder is omitted by sensing directlythe passing of the rolling element, a lower cost can be achieved. Thepresent embodiment intends to implement such structure.

In the case of the present embodiment, each of the revolution speedsensors 21 a, 21 b has magnetic sensing elements 41 provided to opposeto the rolling elements 9 a, 9 b respectively, and a permanent magnet 42putbetween the magnetic sensing elements 41 and provided on the oppositeside to the rolling elements 9 a, 9 b respectively. These rollingelements 9 a, 9 b are made of magnetic material such as the bearingsteal, or the like.

In the case of the present embodiment having such structure, a quantityof magnetic fluxes passing through the magnetic sensing elements 41 isincreased at an instance when the rolling elements 9 a, 9 b pass invicinity of the magnetic sensing elements 41, while a quantity ofmagnetic fluxes passing through the magnetic sensing elements 41 isdecreased while the rolling elements 9 a, 9 b are positioned at remoteportions from the magnetic sensing elements 41. Also, sincecharacteristics of the magnetic sensing elements 41 are changed based onthe change in this quantity of magnetic fluxes, the revolution speed ofthe rolling elements 9 a, 9 b can be measured by measuring a period ofsuch change of the characteristics (or a frequency).

In this case, when these rolling elements 9 a, 9 b are made ofnon-magnetic material such as ceramics, or the like, a density of themagnetic fluxes passing through the magnetic sensing elements 41 can bechanged with the revolution motion of the rolling elements 9 a, 9 b byplating magnetic material on the surface, embedding the magneticmaterial in the inside of the ceramics, or the like.

Also, in the illustrated example, the revolution speed sensors 21 a, 21b are arranged between the rows of the rolling elements 9 a, 9 b. Butfitted positions of the revolution speed sensors 21 a, 21 b are notlimited to the space between these rows. For example, the revolutionspeed sensors 21 a, 21 b may be provided at both end positions of theouter ring 1 in the axial direction to put the rolling elements 9 a, 9 bfrom both sides in the axial direction.

In this case, structures of the rotational speed encoder 13 a and therotational speed sensor 15 b used to sense the rotational speed of thehub 2 are not particularly limited. Like the above embodiments, variousstructures known in the related art can be employed.

Eleventh Embodiment

FIGS. 32 and 33 show an eleventh embodiment of the present invention. Inthe case of the present embodiment, since at least one sensor out of therotational speed sensor 15 b and the revolution speed sensors 21 a, 21 bis constructed by the passive magnetic sensor, reduction in a cost isintended. In other words, if the active type magnetic sensor is used asrespective sensors 15 b, 21 a, 21 b constituting theloadmeasuringdevice, such structure has an advantage that the rotationalspeed and in turn the load can be measured stably from a low speed to ahigh speed, but such a problem exists that a cost of the magnetic sensoris slightly increased. Therefore, in the case of the present embodiment,cost reduction is intended by using the passive type magnetic sensor,which is constructed by winding a coil 44 round a yoke 43 (same meaningas a stator or a pole piece) made of magnetic material, as at least anyone sensor out of respective sensors 15 b, 21 a, 21 b.

As the passive type magnetic sensor out of respective sensors 15 b, 21a, 21 b, the revolution speed sensors 21 a, 21 b shown in FIG. 32 may beselected or the rotational speed sensor 15 b shown in FIG. 33 may beselected. The rotational speed sensor 15 b is formed of the active typemagnetic sensor in the structure shown in FIG. 32, while a pair ofrevolution speed sensors 21 a, 21 b are formed of the active typemagnetic sensor in the structure shown in FIG. 33. In this case, in thecombination of the passive type magnetic sensor and the encoder, thepermanent magnet is not provided on the sensor side when the encoder isformed of the permanent magnet. In contrast, when the permanent magnetis provided on the sensor side, the encoder is made of mere magneticmaterial (not the permanent magnet) and the magnetic characteristic ischanged alternately at an equal interval along the circumferentialdirection. In this case, a structure of the passive type magnetic sensoris not particularly restricted and a variety of structures such as sticktype, ring-like type, or the like, known in the related art may be used.In addition, it is selected in response to the requiredperformance thatthe revolution speed sensors 21 a, 21 b shown in FIG. 32 shouldbeselected as the passive type magnetic sensor or that the rotationalspeed sensor 15 b shown in FIG. 33 should be selected as the passivetype magnetic sensor

For example, it is preferable that, when reduction in measurement of theaxial load is mainly considered, the revolution speed sensors 21 a, 21 bshown in FIG. 32 should be constructed as the passive type magneticsensor. In other words, since the axial load is generated when therevolution speed of the rolling elements 9 a, 9 b is high such as thelane change during the high-speed traveling, or the like, in many casesthere is caused no problem in practical use even though the passive typemagnetic sensor whose output voltage becomes low during the low-speedrunning is used as the revolution speed sensors 21 a, 21 b.

On the contrary, in case installing spaces of the revolution speedsensors 21 a, 21 b are limited, fort example, intervals between the rowsof the rolling elements 9 a, 9 b are narrow, or the like, these sensorsare formed of the active type magnetic sensor that can constitute therevolution speed sensors 21 a, 21 b in a small size, as shown in FIG.33, whereas the rotational speed sensor 15 b whose installing space hasa margin is constructed by the passive type ring-like magnetic sensor.Other structures and operations are similar to foregoing embodiments.

Twelfth Embodiment

FIGS. 34 to 36 show a twelfth embodiment of the present invention. Inthe case of the present embodiment, at least one sensor out of therevolution speed sensors 21 a, 21 b and the rotational speed sensor 15 bis constructed as a resolver. The resolver is composed of rotors 45fixed to members such as the retainers 22 a, 22 b, the hub 2, etc. tosense the rotational speed, and stators 46 fitted/fixed to the fixedouter ring 1 directly or via the cover 14 in a state that such statorsare arranged concentrically with the rotors 45 around the rotors 45. Therotors 45 may be composed of an eccentric rotor. In this case, it ispreferable that, if such rotor is composed of a elliptical rotor, atriangle riceball type, or the like, to have a point-symmetrical shape,not only imbalance of the rotation can be reduced but also the number ofpulses per revolution can be increased.

As described above, if the active type magnetic sensor is used as thespeed sensor, the revolution speed can be measured precisely up to thelow-speed range, nevertheless the number of times of change in theoutput of the magnetic sensor per one revolution of the encoder isreduced and therefore a resolving power in the velocity sensing is notalways enhanced. In contrast, if the resolver is used as the speedsensor, the number of times of change in the output (number of pulses)per one revolution of the rotors 45 can be increased rather than theactive type magnetic sensor, and a resolving power in the velocitysensing is enhanced and in turn a responsibility of the load calculationcan be accelerated. Also, since the resolver main body is constructedonly by a coil and a core (stator), the structure can be made simple andthere liability can be easily assured. In this case, a sensed signal ofthe resolver is input into an R/D converter and then taken out as apulse signal that is changed at a frequency that is in proportion to thespeed.

It is selected appropriately according to the required performance whichone of the revolution speed sensors 21 a, 21 b and the rotational speedsensor 15 b should be constructed as the resolver. In the structureshown in FIG. 34, in order to sense the revolution speed of the rollingelements 9 a, 9 b in respective rows, the rotational speeds of a pair ofretainers 22 a, 22 b are sensed by the resolver and also the rotationalspeed of the hub 2 is sensed by the magnetic sensor. Also, in thestructure shown in FIG. 35, the rotational speed of the hub 2 is sensedby the resolver and also the rotational speeds of a pair of retainers 22a, 22 b are sensed by the magnetic sensor. In addition, in the structureshown in FIG. 36, the rotational speeds of a pair of retainers 22 a, 22b and the rotational speed of the hub 2 are sensed by the resolver. Theevent that structures of the resolver and the magnetic sensors and theirfitted positions are not limited to- those illustrated, the event that avariety of materials for the rotor and the encoder can be employed, etc.are similar to the case in foregoing embodiments.

Thirteenth Embodiment

In this case, as apparent from above explanation, the axial load appliedto the rolling bearing unit can be calculated based on a ratio of therevolution speeds of the rolling elements in double rows independent ofchange in the rotational speed of the hub. In this case, because onlydivision of the revolution speeds of the double rows is calculated, therotational speed of the hub is not needed in load calculation. Incontrast, because the rotational speed of the hub can be calculated fromthe revolution speeds of the rolling elements in double rows, the sensorfor sensing the rotational speed of the hub, which is needed to controlthe ABS or the TCS, can be omitted. More particularly, if an averagevalue of the revolution speeds of the rolling elements in double rows isused as the rotational speed of the hub, a precision enough to controlthe ABS or the TCS in practical use can be assured. In this case, anaction of the axial load maybe considered as a factor for changing therevolution speeds of the rolling elements in double rows. In such event,since the average value of the revolution speeds of the rolling elementsin double rows is not so affected by the axial load, a measuringprecision of the rotational speed is never degraded to such an extentthat the precision becomes an issue in practical use. The reason forthis is that, as described above, even if the revolution speed in onerow is increased by the axial load, the revolution speed in the otherrow is changed toward the smaller direction. The revolution speeds indouble rows are also changed by the radial load, but such change issmall in contrast to the influence of the axial load. Therefore, in somecase such change can be neglected according to the precision required tocontrol the ABS or the TCS.

Although the invention has been described in detail with reference tospecific embodiments, it is obvious to those skilled in the art thatvarious changes and modifications can be made without departing from thespirit and scope thereof.

This application is based on Japanese Patent Application Nos.2003-144942 filed on May 22, 2003, 2003-171715 filed on Jun. 17, 2003,2003-172483 filed on Jun. 17, 2003 and 2004-007655 filed on Jan. 15,2004, the contents of which are incorporated herein by reference.

1. A load measuring device for a rolling bearing unit comprising: astationary ring having two rows of raceways; a rotating ring arrangedconcentrically with the stationary ring, the rotating ring having tworows of raceways which are formed respectively to be opposite to theraceways of the stationary ring; a plurality of rolling elementsprovided rotatably between the raceways of the stationary ring and therotating ring, wherein contact angles of the rolling elements aredirected mutually oppositely between a pair of raceways formed on thestationary ring and the rotating ring which are opposite to each otherand the other pair of raceways formed on the stationary ring and therotating ring which are opposite to each other; a pair of revolutionspeed sensors for sensing revolution speeds of the rolling elements inthe two rows respectively; and a calculator for calculating a loadapplied between the stationary ring and the rotating ring based onsensed signals fed the revolution speed sensors.
 2. A load measuringdevice for a rolling bearing unit according to claim 1, furthercomprising: a rotational speed sensor for sensing a rotational speed ofthe rotating ring.
 3. (canceled)
 4. A load measuring device for arolling bearing unit according to claim 2, wherein at least one sensorof the pair of revolution speed sensors and the rotational speed sensoris a resolver.
 5. A load measuring device for a rolling bearing unitaccording to claims 2, wherein the pair of revolution speed sensors andthe rotational speed sensor are provided at an interval in an axialdirection of the stationary ring so as to put the rolling elements inone row between the pair of revolution speed sensors and the rotationalspeed sensor.
 6. (canceled)
 7. A load measuring device for a rollingbearing unit according to claims 2, wherein the pair of revolution speedsensors and the rotational speed sensor are fitted to a top end portionof a single sensor unit fixed to the stationary ring between a pair ofrows of the rolling elements, and a fitted position of the rotationalspeed sensor is deviated closer to a rotating ring side than therevolution speed sensors in a diameter direction of the stationary ring.8. (canceled)
 9. (canceled)
 10. A load measuring device for a rollingbearing unit according to claim 1, wherein a control to be executedbased on a rotational speed of the rotating ring is executed based onthe rotational speed of the rotating ring, which is estimated based onthe sensed signal of at least one revolution speed sensor out of therevolution speed sensors.
 11. A load measuring device for a rollingbearing unit according to claim 10, wherein an average value of therevolution speeds of the rolling elements in the two rows, which iscalculated based on the sensed signals of the pair of revolution speedsensors, is used as an estimated value of the rotational speed of therotating ring.
 12. (canceled)
 13. A load measuring device for a rollingbearing unit according to claim 1, wherein the calculator calculates theradial load applied between the stationary ring and the rotating ringbased on a sum of the revolution speed of the rolling elements in onerow and the revolution speed of the rolling elements in the other row.14. A load measuring device for a rolling bearing unit according toclaim 1, further comprising: a rotational speed sensor for sensing arotational speed of the rotating ring, wherein the calculator calculatesthe radial load applied between the stationary ring and the rotatingring based on a sensed signal fed from the rotational speed sensor andsensed signals fed from the revolution speed sensors.
 15. A loadmeasuring device for a rolling bearing unit according to claim 14,wherein the calculator calculates the radial load applied between thestationary ring and the rotating ring based on a ratio of: the sum of(a) the revolution speed of the rolling elements in one row and (b) therevolution speed of the rolling elements in the other row, and therotational speed of the rotating ring.
 16. A load measuring device for arolling bearing unit according to claim 14, wherein the calculatorcalculates the radial load applied between the stationary ring and therotating ring based on a ratio of: a product of (a) the revolution speedof the rolling elements in one row and (b) the revolution speed of therolling elements in the other row, and a square of the rotational speedof the rotating ring.
 17. (canceled)
 18. A load measuring device for arolling bearing unit according to claim 1, wherein the calculatorcalculates the axial load applied between the stationary ring and therotating ring based on a ratio of the revolution speed of the rollingelements in one row and the revolution speed of the rolling elements inthe other row.
 19. A load measuring device for a rolling bearing unitaccording to claim 1, wherein the calculator calculates the radial loadapplied between the stationary ring and the rotating ring based on adifference between the revolution speed of the rolling elements in onerow and the revolution speed of the rolling elements in the other row.20. A load measuring device for a rolling bearing unit according toclaim 1, further comprising: a rotational speed sensor for sensing arotational speed of the rotating ring, wherein the calculator calculatesthe axial load applied between the stationary ring and the rotating ringbased on a sensed signal fed from the rotational speed sensor and sensedsignals fed from the revolution speed sensors.
 21. A load measuringdevice for a rolling bearing unit according to claim 20, where in thecalculator calculates the axial load applied between the stationary ringand the rotating ring based on a ratio of: the difference between (a)the revolution speed of the rolling elements in one row and (b) therevolution speed of the rolling elements in the other row, and therotational speed of the rotating ring.
 22. A load measuring device for arolling bearing unit according to claim 1, wherein the calculatorcalculates the axial load applied between the stationary ring and therotating ring based on a synthesized signal obtained by synthesizing asignal representing the revolution speed of the rolling elements in onerow and a signal representing the revolution speed of the rollingelements in the other row.
 23. A load measuring device for a rollingbearing unit according to claim 22, wherein the calculator calculatesthe axial load based on any one of a period and a frequency of a swellof the synthesized signal.
 24. A load measuring device for a rollingbearing unit according to claim 22, further comprising: a rotationalspeed sensor for sensing a rotational speed of the rotating ring,wherein the calculator calculates the axial load based on a ratio of anyone of a period and a frequency of a swell of the synthesized signal andthe rotational speed of the rotating ring.
 25. (canceled)
 26. (canceled)27. A load measuring device for a rolling bearing unit according toclaims 1, wherein the revolution speeds of the rolling elements in thetwo rows are measured as rotational speeds of retainers for holdingrespective rolling elements.
 28. (canceled)
 29. (canceled) 30.(canceled)
 31. (canceled)
 32. (canceled)
 33. A load measuring device fora rolling bearing unit according to any one of claims 1, furthercomprising: a comparator for comparing contact angles of the rollingelements in each row, which are calculated by the calculator calculatesin a course of calculation of the revolution speeds of the rollingelements in each row, with a normal value, wherein an alarm is generatedwhen the comparator decides that the contact angles are out of a normalrange.
 34. A load measuring rolling bearing unit comprising: astationary ring having two rows of raceways; a rotating ring arrangedconcentrically with the stationary ring, the rotating ring having tworows of raceways which are formed respectively to be opposite to theraceways of the stationary ring; a plurality of rolling elementsprovided rotatably between the raceways of the stationary ring and therotating ring, wherein contact angles of the rolling elements aredirected mutually oppositely between a pair of raceways formed on thestationary ring and the rotating ring which are opposite to each otherand the other pair of raceways formed on the stationary ring and therotating ring which are opposite to each other; and a pair of revolutionspeed sensors for sensing revolution speeds of the rolling elements inthe two rows respectively.
 35. (canceled)
 36. A load measuring rollingbearing unit according to claim 3, further comprising: a calculator forcalculating a load applied between the stationary ring and the rotatingring based on sensed signals fed the revolution speed sensors.
 37. Aload measuring rolling bearing unit according to claim 3, furthercomprising: a rotational speed sensor for sensing rotational speed ofthe rotating ring.
 38. A load measuring rolling bearing unit accordingto claim 3, further comprising: a calculator for calculating a loadapplied between the stationary ring and the rotating ring based onsensed signals fed the revolution speed sensors and a sensed signal fedfrom the rotational speed sensor.
 39. (canceled)
 40. (canceled)
 41. Aload measuring rolling bearing unit according to claims 3, furthercomprising: a comparator for comparing contact angles of the rollingelements in each row, which are calculated by the calculator in a courseof calculation of the revolution speeds of the rolling elements in eachrow, with a normal value, wherein an alarm is generated when thecomparator decides that the contact angles are out of a normal range.42. (canceled)